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/UefiLib/Console.c

@@ -390,7 +390,7 @@ VOID
 EFIAPI
 CreatePopUp (
   IN  UINTN          Attribute,
-  OUT EFI_INPUT_KEY  *Key,      OPTIONAL
+  OUT EFI_INPUT_KEY  *Key       OPTIONAL,
   ...
   )
 {