ShellPkg/UefiShellAcpiViewCommandLib: Fix ECC issues

1. Separate variable definition and initialization.
2. Make the variable naming following Edk2 rule.

V2: Remove the updates of guard macros in header files.

Cc: Sami Mujawar <sami.mujawar@arm.com>
Cc: Evan Lloyd <evan.lloyd@arm.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>

ShellPkg/Library/UefiShellAcpiViewCommandLib/Parsers/Madt/MadtParser.c

@@ -197,7 +197,9 @@ ParseAcpiMadt (
 {
   UINT32 Offset;
   UINT8* InterruptContollerPtr;
-  UINT32 GICDCount = 0;
+  UINT32 GICDCount;
+
+  GICDCount = 0;
 
   if (!Trace) {
     return;