audio: changed some SDL_memset() calls to SDL_zero(), other minor corrections.

src/audio/sun/SDL_sunaudio.c

@@ -212,7 +212,7 @@ SUNAUDIO_OpenDevice(_THIS, void *handle, const char *devname, int iscapture)
     if (this->hidden == NULL) {
         return SDL_OutOfMemory();
     }
-    SDL_memset(this->hidden, 0, (sizeof *this->hidden));
+    SDL_zerop(this->hidden);
 
     /* Open the audio device */
     this->hidden->audio_fd = open(devname, flags, 0);