SI_DeviceGBA: Make GBASockServer's constructor explicit

Prevents potential implicit construction scenarios involving ints.

Source/Core/Core/HW/SI/SI_DeviceGBA.h

@@ -21,7 +21,7 @@ void GBAConnectionWaiter_Shutdown();
 class GBASockServer
 {
 public:
-  GBASockServer(int _iDeviceNumber);
+  explicit GBASockServer(int _iDeviceNumber);
   ~GBASockServer();
 
   void Disconnect();