ControllerInterface: Make UpdateInput / UpdateOutput return void

The return values here have never been checked, so it doesn't make sense
to return a value to begin with.

Source/Core/InputCommon/ControllerInterface/Xlib/XInput2.h

@@ -98,7 +98,7 @@ private:
 	void UpdateCursor();
 
 public:
-	bool UpdateInput() override;
+	void UpdateInput() override;
 
 	KeyboardMouse(Window window, int opcode, int pointer_deviceid, int keyboard_deviceid);
 	~KeyboardMouse();