Call Do for every member of SCPFifoStruct individually

We need this because VS currently doesn't consider
std::is_trivially_copyable<typename
std::remove_volatile<SCPFifoStruct>::type>::value
to be true and because no compiler should consider it
to be true if we replace the volatiles with atomics.

Source/Core/VideoCommon/CommandProcessor.h

@@ -38,6 +38,8 @@ struct SCPFifoStruct
 
   volatile u32 bFF_LoWatermark;
   volatile u32 bFF_HiWatermark;
+
+  void DoState(PointerWrap& p);
 };
 
 // This one is shared between gfx thread and emulator thread.