StandaloneMmPkg: Change OPTIONAL keyword usage style

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3760

Update all use of ', OPTIONAL' to ' OPTIONAL,' for function params.

Cc: Andrew Fish <afish@apple.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Michael Kubacki <michael.kubacki@microsoft.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>

StandaloneMmPkg/Library/StandaloneMmCoreHobLib/X64/StandaloneMmCoreHobLib.c

@@ -236,7 +236,7 @@ BuildFv3Hob (
   IN          UINT64                      Length,
   IN          UINT32                      AuthenticationStatus,
   IN          BOOLEAN                     ExtractedFv,
-  IN CONST    EFI_GUID                    *FvName, OPTIONAL
+  IN CONST    EFI_GUID                    *FvName  OPTIONAL,
   IN CONST    EFI_GUID                    *FileName OPTIONAL
   )
 {