EmulatorPkg: 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: Ray Ni <ray.ni@intel.com>

EmulatorPkg/EmuGopDxe/GopScreen.c

@@ -184,7 +184,7 @@ EFI_STATUS
 EFIAPI
 EmuGopBlt (
   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,
@@ -407,4 +407,3 @@ Returns:
 {
   EmuGopDestructor (Context);
 }
-