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/QemuVideoDxe/Gop.c

@@ -239,7 +239,7 @@ EFI_STATUS
 EFIAPI
 QemuVideoGraphicsOutputBlt (
   IN  EFI_GRAPHICS_OUTPUT_PROTOCOL          *This,
-  IN  EFI_GRAPHICS_OUTPUT_BLT_PIXEL         *BltBuffer, OPTIONAL
+  IN  EFI_GRAPHICS_OUTPUT_BLT_PIXEL         *BltBuffer  OPTIONAL,
   IN  EFI_GRAPHICS_OUTPUT_BLT_OPERATION     BltOperation,
   IN  UINTN                                 SourceX,
   IN  UINTN                                 SourceY,
@@ -413,5 +413,3 @@ Returns:
 
   return EFI_SUCCESS;
 }
-
-