Fix -Wundef warnings due to use of unguarded SDL_AUDIO_DRIVER_PSP

src/audio/SDL_audio.c

@@ -70,7 +70,7 @@ static const AudioBootStrap *const bootstrap[] = {
 #ifdef SDL_AUDIO_DRIVER_PS2
     &PS2AUDIO_bootstrap,
 #endif
-#if SDL_AUDIO_DRIVER_PSP
+#ifdef SDL_AUDIO_DRIVER_PSP
     &PSPAUDIO_bootstrap,
 #endif
 #if SDL_AUDIO_DRIVER_VITA

src/audio/psp/SDL_pspaudio.c

@@ -20,7 +20,7 @@
 */
 #include "SDL_internal.h"
 
-#if SDL_AUDIO_DRIVER_PSP
+#ifdef SDL_AUDIO_DRIVER_PSP
 
 #include <stdio.h>
 #include <string.h>