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/Include/Protocol/Rng.h

@@ -125,7 +125,7 @@ typedef
 EFI_STATUS
 (EFIAPI *EFI_RNG_GET_RNG) (
   IN EFI_RNG_PROTOCOL            *This,
-  IN EFI_RNG_ALGORITHM           *RNGAlgorithm, OPTIONAL
+  IN EFI_RNG_ALGORITHM           *RNGAlgorithm  OPTIONAL,
   IN UINTN                       RNGValueLength,
   OUT UINT8                      *RNGValue
   );