OvmfPkg: 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: Andrew Fish <afish@apple.com>

OvmfPkg/Library/LockBoxLib/LockBoxLib.c

@@ -291,7 +291,7 @@ RETURN_STATUS
 EFIAPI
 RestoreLockBox (
   IN  GUID                        *Guid,
-  IN  VOID                        *Buffer, OPTIONAL
+  IN  VOID                        *Buffer  OPTIONAL,
   IN  OUT UINTN                   *Length  OPTIONAL
   )
 {