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/games/gitadora/gitadora.h

@@ -20,6 +20,7 @@ namespace games::gitadora {
     extern std::optional<socd::SocdAlgorithm> PICK_ALGO;
     extern std::optional<uint8_t> ARENA_WINDOW_COUNT;
     extern std::optional<std::string> ASIO_DRIVER;
+    extern bool ALLOW_REALTEK_AUDIO;
 
     class GitaDoraGame : public games::Game {
     public: