ArmPkg: Fix Ecc error 5007 in ArmDisassemblerLib

This patch fixes the following Ecc reported error:
There should be no initialization of a variable as
part of its declaration

Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

ArmPkg/Library/ArmDisassemblerLib/ArmDisassembler.c

@@ -158,7 +158,7 @@ DisassembleArmInstruction (
   IN  BOOLEAN   Extended
   )
 {
-  UINT32    OpCode = **OpCodePtr;
+  UINT32    OpCode;
   CHAR8     *Type, *Root;
   BOOLEAN   I, P, U, B, W, L, S, H;
   UINT32    Rn, Rd, Rm;
@@ -166,6 +166,8 @@ DisassembleArmInstruction (
   UINT32    Index;
   UINT32    shift_imm, shift;
 
+  OpCode = **OpCodePtr;
+
   I = (OpCode & BIT25) == BIT25;
   P = (OpCode & BIT24) == BIT24;
   U = (OpCode & BIT23) == BIT23;