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/apphandler.cpp b/apphandler.cpp
index 6cdd78f..0577c07 100644
--- a/apphandler.cpp
+++ b/apphandler.cpp
@@ -578,10 +578,10 @@
               uint16_t, // Product ID
               uint32_t  // AUX info
               >
-    ipmiAppGetDeviceId(ipmi::Context::ptr ctx)
+    ipmiAppGetDeviceId([[maybe_unused]] ipmi::Context::ptr ctx)
 {
     int r = -1;
-    Revision rev = {0};
+    Revision rev = {0, 0, 0, 0};
     static struct
     {
         uint8_t id;
@@ -1630,8 +1630,9 @@
  *   - readData - i2c response data
  */
 ipmi::RspType<std::vector<uint8_t>>
-    ipmiMasterWriteRead(bool isPrivateBus, uint3_t busId, uint4_t channelNum,
-                        bool reserved, uint7_t slaveAddr, uint8_t readCount,
+    ipmiMasterWriteRead([[maybe_unused]] bool isPrivateBus, uint3_t busId,
+                        [[maybe_unused]] uint4_t channelNum, bool reserved,
+                        uint7_t slaveAddr, uint8_t readCount,
                         std::vector<uint8_t> writeData)
 {
     if (reserved)