cleanup init functions of audio

- use SDL_bool if possible
- assume NULL/SDL_FALSE filled impl
- skip zfill of current_audio at the beginning of SDL_AudioInit (done before the init() calls)

src/audio/sun/SDL_sunaudio.c

@@ -394,7 +394,7 @@ snd2au(int sample)
     return (mask & sample);
 }
 
-static int
+static SDL_bool
 SUNAUDIO_Init(SDL_AudioDriverImpl * impl)
 {
     /* Set the function pointers */
@@ -405,13 +405,13 @@ SUNAUDIO_Init(SDL_AudioDriverImpl * impl)
     impl->GetDeviceBuf = SUNAUDIO_GetDeviceBuf;
     impl->CloseDevice = SUNAUDIO_CloseDevice;
 
-    impl->AllowsArbitraryDeviceNames = 1;
+    impl->AllowsArbitraryDeviceNames = SDL_TRUE;
 
-    return 1; /* this audio target is available. */
+    return SDL_TRUE; /* this audio target is available. */
 }
 
 AudioBootStrap SUNAUDIO_bootstrap = {
-    "audio", "UNIX /dev/audio interface", SUNAUDIO_Init, 0
+    "audio", "UNIX /dev/audio interface", SUNAUDIO_Init, SDL_FALSE
 };
 
 #endif /* SDL_AUDIO_DRIVER_SUNAUDIO */