MdeModulePkg/DxeCapsuleLibFmp: Improve comparisons in CapsuleOnDisk.c

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2028

Non-Boolean comparisons should use a compare operator
(==, !=, >, < >=, <=).

Signed-off-by: Wei6 Xu <wei6.xu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Hao A Wu <hao.a.wu@intel.com>

MdeModulePkg/Library/DxeCapsuleLibFmp/CapsuleOnDisk.c

@@ -127,7 +127,7 @@ UpperCaseString (
 {
   CHAR16  *Cptr;
 
-  for (Cptr = Str; *Cptr; Cptr++) {
+  for (Cptr = Str; *Cptr != L'\0'; Cptr++) {
     if (L'a' <= *Cptr && *Cptr <= L'z') {
       *Cptr = *Cptr - L'a' + L'A';
     }