gitadora: (arena model) flip realtek option (#733)

## Link to GitHub Issue or related Pull Request, if one exists
#730 

## Description of change
Flip the option - enable the Realtek hack by default, unless the user
chooses not to.

## Testing
Tested ASIO path and WASAPI path. WASAPI path should be unaffected as
the game just picks the default audio device.

src/spice2x/hooks/audio/backends/mmdevice/null_device.cpp

@@ -27,7 +27,7 @@ static const PROPERTYKEY PKEY_DEVICE_FRIENDLY_NAME_LOCAL = {
 };
 
 bool null_render_device_enabled() {
-    return hooks::audio::FAKE_REALTEK_RENDER_DEVICE;
+    return hooks::audio::INJECT_FAKE_REALTEK_AUDIO;
 }
 
 // duplicate a wide string into CoTaskMem so the caller can free it with