emu_window: Pass OnMinimalClientAreaChangeRequest argument by copy

There's no performance improvement in passing an unsigned pair by
reference.

src/yuzu_cmd/emu_window/emu_window_sdl2.h

@@ -50,8 +50,7 @@ protected:
     void Fullscreen();
 
     /// Called when a configuration change affects the minimal size of the window
-    void OnMinimalClientAreaChangeRequest(
-        const std::pair<unsigned, unsigned>& minimal_size) override;
+    void OnMinimalClientAreaChangeRequest(std::pair<unsigned, unsigned> minimal_size) override;
 
     /// Is the window still open?
     bool is_open = true;