ArmPkg: Fix Ecc error 3002 in CompilerIntrinsicsLib

This patch fixes the following Ecc reported error:
Non-Boolean comparisons should use a compare operator
(==, !=, >, < >=, <=)

Brackets are also added to comply to with the coding
standard.

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

ArmPkg/Library/CompilerIntrinsicsLib/memset_ms.c

@@ -1,6 +1,7 @@
 //------------------------------------------------------------------------------
 //
 // Copyright (c) 2017, Pete Batard. All rights reserved.<BR>
+// Copyright (c) 2021, Arm Limited. All rights reserved.<BR>
 //
 // SPDX-License-Identifier: BSD-2-Clause-Patent
 //
@@ -19,8 +20,9 @@ void *memset(void *s, int c, size_t n)
 {
   unsigned char *d = s;
 
-  while (n--)
+  while (n-- != 0) {
     *d++ = (unsigned char)c;
+  }
 
   return s;
 }