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/Drivers/StandaloneMmCpu/EventHandle.c

@@ -215,8 +215,8 @@ EFI_STATUS
 EFIAPI
 PiMmCpuTpFwRootMmiHandler (
   IN     EFI_HANDLE               DispatchHandle,
-  IN     CONST VOID               *Context,        OPTIONAL
-  IN OUT VOID                     *CommBuffer,     OPTIONAL
+  IN     CONST VOID               *Context         OPTIONAL,
+  IN OUT VOID                     *CommBuffer      OPTIONAL,
   IN OUT UINTN                    *CommBufferSize  OPTIONAL
   )
 {