MdePkg: 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>

MdePkg/Library/DxePcdLib/DxePcdLib.c

@@ -829,7 +829,7 @@ LibPcdSetExBoolS (
 VOID
 EFIAPI
 LibPcdCallbackOnSet (
-  IN CONST GUID               *Guid,       OPTIONAL
+  IN CONST GUID               *Guid        OPTIONAL,
   IN UINTN                    TokenNumber,
   IN PCD_CALLBACK             NotificationFunction
   )
@@ -862,7 +862,7 @@ LibPcdCallbackOnSet (
 VOID
 EFIAPI
 LibPcdCancelCallback (
-  IN CONST GUID               *Guid,       OPTIONAL
+  IN CONST GUID               *Guid        OPTIONAL,
   IN UINTN                    TokenNumber,
   IN PCD_CALLBACK             NotificationFunction
   )
@@ -901,7 +901,7 @@ LibPcdCancelCallback (
 UINTN
 EFIAPI
 LibPcdGetNextToken (
-  IN CONST GUID               *Guid,       OPTIONAL
+  IN CONST GUID               *Guid        OPTIONAL,
   IN UINTN                    TokenNumber
   )
 {
@@ -1218,4 +1218,3 @@ LibPcdGetSku (
 {
   return GetPiPcdInfoProtocolPointer()->GetSku ();
 }
-