Fix -Wundef warnings due to use of unguarded SDL_AUDIO_DRIVER_HAIKU

src/audio/SDL_audio.c

@@ -52,7 +52,7 @@ static const AudioBootStrap *const bootstrap[] = {
 #ifdef SDL_AUDIO_DRIVER_DSOUND
     &DSOUND_bootstrap,
 #endif
-#if SDL_AUDIO_DRIVER_HAIKU
+#ifdef SDL_AUDIO_DRIVER_HAIKU
     &HAIKUAUDIO_bootstrap,
 #endif
 #if SDL_AUDIO_DRIVER_COREAUDIO

src/audio/haiku/SDL_haikuaudio.cc

@@ -20,7 +20,7 @@
 */
 #include "SDL_internal.h"
 
-#if SDL_AUDIO_DRIVER_HAIKU
+#ifdef SDL_AUDIO_DRIVER_HAIKU
 
 /* Allow access to the audio stream on Haiku */