MdeModulePkg: 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: Liming Gao <gaoliming@byosoft.com.cn>

MdeModulePkg/Universal/PCD/Pei/Service.c

@@ -298,7 +298,7 @@ PeiGetPcdInfo (
 EFI_STATUS
 PeiRegisterCallBackWorker (
   IN  UINTN                       ExTokenNumber,
-  IN  CONST EFI_GUID              *Guid, OPTIONAL
+  IN  CONST EFI_GUID              *Guid  OPTIONAL,
   IN  PCD_PPI_CALLBACK            CallBackFunction,
   IN  BOOLEAN                     Register
 )
@@ -529,7 +529,7 @@ GetHiiVariable (
 VOID
 InvokeCallbackOnSet (
   UINTN             ExTokenNumber,
-  CONST EFI_GUID    *Guid, OPTIONAL
+  CONST EFI_GUID    *Guid  OPTIONAL,
   UINTN             TokenNumber,
   VOID              *Data,
   UINTN             Size