MdeModulePkg: 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>

MdeModulePkg/Bus/Pci/PciSioSerialDxe/Serial.c

@@ -421,7 +421,7 @@ CreateSerialDevice (
   IN BOOLEAN                        CreateControllerNode,
   IN UINT32                         Instance,
   IN PARENT_IO_PROTOCOL_PTR         ParentIo,
-  IN PCI_SERIAL_PARAMETER           *PciSerialParameter, OPTIONAL
+  IN PCI_SERIAL_PARAMETER           *PciSerialParameter  OPTIONAL,
   IN PCI_DEVICE_INFO                *PciDeviceInfo       OPTIONAL
   )
 {