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/PciHotPlugInitDxe/PciHotPlugInit.c

@@ -489,7 +489,7 @@ InitializeRootHpc (
   IN  EFI_PCI_HOT_PLUG_INIT_PROTOCOL *This,
   IN  EFI_DEVICE_PATH_PROTOCOL       *HpcDevicePath,
   IN  UINT64                         HpcPciAddress,
-  IN  EFI_EVENT                      Event, OPTIONAL
+  IN  EFI_EVENT                      Event  OPTIONAL,
   OUT EFI_HPC_STATE                  *HpcState
   )
 {