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/Variable/RuntimeDxe/RuntimeDxeUnitTest/VariableLockRequestToLockUnitTest.c

@@ -86,7 +86,7 @@ EFIAPI
 StubGetVariableNull (
   IN     CHAR16    *VariableName,
   IN     EFI_GUID  *VendorGuid,
-  OUT    UINT32    *Attributes,  OPTIONAL
+  OUT    UINT32    *Attributes   OPTIONAL,
   IN OUT UINTN     *DataSize,
   OUT    VOID      *Data         OPTIONAL
   )