SignedCapsulePkg: 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: Jian J Wang <jian.j.wang@intel.com>

SignedCapsulePkg/Universal/RecoveryModuleLoadPei/RecoveryModuleLoadPei.c

@@ -241,7 +241,7 @@ IsValidCapsuleHeader (
 EFI_STATUS
 ValidateFmpCapsule (
   IN EFI_CAPSULE_HEADER *CapsuleHeader,
-  OUT BOOLEAN           *IsSystemFmp, OPTIONAL
+  OUT BOOLEAN           *IsSystemFmp  OPTIONAL,
   OUT UINT16            *EmbeddedDriverCount OPTIONAL
   )
 {