Use structs for config callback IDs

This way you can't mix up regular config callback IDs and CPU thread
config callback IDs. (It would be rather bad if you did!)

Source/Core/Core/FifoPlayer/FifoPlayer.h

@@ -10,6 +10,7 @@
 #include <vector>
 
 #include "Common/Assert.h"
+#include "Common/Config/Config.h"
 #include "Core/FifoPlayer/FifoDataFile.h"
 #include "Core/PowerPC/CPUCoreBase.h"
 #include "VideoCommon/CPMemory.h"
@@ -189,7 +190,7 @@ private:
 
   CallbackFunc m_FileLoadedCb = nullptr;
   CallbackFunc m_FrameWrittenCb = nullptr;
-  size_t m_config_changed_callback_id;
+  Config::ConfigChangedCallbackID m_config_changed_callback_id;
 
   std::unique_ptr<FifoDataFile> m_File;