cleanup: Remove all warning errors for the Meson build support

Remove all the build warning to prepare for the meson build.
Meson build will be in
https://gerrit.openbmc-project.xyz/c/openbmc/phosphor-host-ipmid/+/47748

Tested:
Ipmi command works fine the cleanup.
```
$ systemctl status phosphor-ipmi-host
● phosphor-ipmi-host.service - Phosphor Inband IPMI
     Loaded: loaded (/lib/systemd/system/phosphor-ipmi-host.service; enabled; vendor preset: enabled)
     Active: active (running) since Thu 1970-01-08 21:20:56 UTC; 21s ago
   Main PID: 24987 (ipmid)
     CGroup: /system.slice/phosphor-ipmi-host.service
             └─24987 /tmp/ipmid

Jan 08 21:20:56 $HOST ipmid[24987]: Registering OEM:[0X002B79], Cmd:[0X30] for Ethstats Commands
Jan 08 21:20:56 $HOST ipmid[24987]: Registering OEM:[0X00C2CF], Cmd:[0X30] for Ethstats Commands
Jan 08 21:20:56 $HOST ipmid[24987]: Registering OEM:[0X002B79], Cmd:[0X32] for Sys Commands
Jan 08 21:20:56 $HOST ipmid[24987]: Registering OEM:[0X002B79], Cmd:[0X02] for I2C
Jan 08 21:20:56 $HOST ipmid[24987]: Registering OEM:[0X00C2CF], Cmd:[0X02] for I2C
Jan 08 21:20:56 $HOST ipmid[24987]: I2C_WHITELIST_CHECK is disabled, do not populate whitelist
Jan 08 21:20:56 $HOST ipmid[24987]: Registering OEM:[0X00C2CF], Cmd:[0X04] for Manual Zone Control
Jan 08 21:20:56 $HOST systemd[1]: Started Phosphor Inband IPMI.
Jan 08 21:20:56 $HOST ipmid[24987]: Loading whitelist filter
Jan 08 21:20:56 $HOST ipmid[24987]: Set restrictedMode = true
(reverse-i-search)`ipmi': systemctl status phosphor-^Cmi-host

$ ipmitool mc info
Device ID                 : 32
Device Revision           : 1
Firmware Revision         : 0.00
IPMI Version              : 2.0
Manufacturer ID           : 7244
Manufacturer Name         : Quanta Computer Inc.
Product ID                : 14426 (0x385a)
Product Name              : Unknown (0x385A)
Device Available          : yes
Provides Device SDRs      : yes
Additional Device Support :
    Sensor Device
    SEL Device
    FRU Inventory Device
    Chassis Device
Aux Firmware Rev Info     :
    0x00
    0x00
    0x00
    0x00
```

Change-Id: I372c9433a274bc633a24d213b7a1bc205531e33d
Signed-off-by: Willy Tu <wltu@google.com>
diff --git a/user_channel/usercommands.cpp b/user_channel/usercommands.cpp
index 7af38b9..901e4a6 100644
--- a/user_channel/usercommands.cpp
+++ b/user_channel/usercommands.cpp
@@ -85,7 +85,7 @@
         return ipmi::responseParmOutOfRange();
     }
 
-    PrivAccess privAccess = {0};
+    PrivAccess privAccess = {};
     if (bitsUpdate)
     {
         privAccess.ipmiEnabled = static_cast<uint8_t>(ipmiEnabled);
@@ -207,7 +207,8 @@
  *  @returns ipmi response
  */
 ipmi::RspType<>
-    ipmiSetUserName(ipmi::Context::ptr ctx, uint6_t id, uint2_t reserved,
+    ipmiSetUserName([[maybe_unused]] ipmi::Context::ptr ctx, uint6_t id,
+                    uint2_t reserved,
                     const std::array<uint8_t, ipmi::ipmiMaxUserName>& name)
 {
     if (reserved)
@@ -238,7 +239,8 @@
  *  @returns ipmi response with 16-byte username
  */
 ipmi::RspType<std::array<uint8_t, ipmi::ipmiMaxUserName>> // user name
-    ipmiGetUserName(ipmi::Context::ptr ctx, uint6_t id, uint2_t reserved)
+    ipmiGetUserName([[maybe_unused]] ipmi::Context::ptr ctx, uint6_t id,
+                    uint2_t reserved)
 {
     if (reserved)
     {
@@ -271,9 +273,9 @@
  *  @returns ipmi response with 16-byte username
  */
 ipmi::RspType<> // user name
-    ipmiSetUserPassword(ipmi::Context::ptr ctx, uint6_t id, bool reserved1,
-                        bool pwLen20, uint2_t operation, uint6_t reserved2,
-                        SecureBuffer& userPassword)
+    ipmiSetUserPassword([[maybe_unused]] ipmi::Context::ptr ctx, uint6_t id,
+                        bool reserved1, bool pwLen20, uint2_t operation,
+                        uint6_t reserved2, SecureBuffer& userPassword)
 {
     if (reserved1 || reserved2)
     {
@@ -404,7 +406,8 @@
               >
     ipmiGetChannelAuthenticationCapabilities(ipmi::Context::ptr ctx,
                                              uint4_t chNum, uint3_t reserved1,
-                                             bool extData, uint4_t privLevel,
+                                             [[maybe_unused]] bool extData,
+                                             uint4_t privLevel,
                                              uint4_t reserved2)
 {
     uint8_t channel =
@@ -522,7 +525,7 @@
         return ipmi::responseParmOutOfRange();
     }
 
-    PayloadAccess payloadAccess = {0};
+    PayloadAccess payloadAccess = {};
     payloadAccess.stdPayloadEnables1[1] = stdPayload1SOL;
 
     return ipmi::response(ipmiUserSetUserPayloadAccess(