ArmPkg: Fix Ecc error 5007 in CompilerIntrinsicsLib

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/CompilerIntrinsicsLib/memset_ms.c

@@ -18,7 +18,9 @@ void* memset(void *, int, size_t);
 #pragma function(memset)
 void *memset(void *s, int c, size_t n)
 {
-  unsigned char *d = s;
+  unsigned char *d;
+
+  d = s;
 
   while (n-- != 0) {
     *d++ = (unsigned char)c;