psu-ng: Change the IBM_VPD checking condition

By default, the IBM_VPD will be defined as 0 (False).
We used the "#ifdef IBM_VPD" to check the define IBM_VPD,
it's not correct completely. The source code of IBM VPD
always runs in both TRUE or FALSE.

Signed-off-by: Chanh Nguyen <chanh@os.amperecomputing.com>
Change-Id: I7e6e9c5c2c62de3a1b7f52d2be1caf6b44f0a2f4
diff --git a/phosphor-power-supply/power_supply.cpp b/phosphor-power-supply/power_supply.cpp
index 02fe779..dbdfb20 100644
--- a/phosphor-power-supply/power_supply.cpp
+++ b/phosphor-power-supply/power_supply.cpp
@@ -267,7 +267,7 @@
 {
     using namespace phosphor::pmbus;
 
-#ifdef IBM_VPD
+#if IBM_VPD
     std::string ccin;
     std::string pn;
     std::string fn;
@@ -291,7 +291,7 @@
     {
         // TODO: non-IBM inventory updates?
 
-#ifdef IBM_VPD
+#if IBM_VPD
         try
         {
             ccin = pmbusIntf->readString(CCIN, Type::HwmonDeviceDebug);