audio: Clean up some CloseDevice() interface details.

- It's now always called if device->hidden isn't NULL, even if OpenDevice()
  failed halfway through. This lets implementation code not have to clean up
  itself on every possible failure point; just return an error and SDL will
  handle it for you.

- Implementations can assume this->hidden != NULL and not check for it.

- implementations don't have to set this->hidden = NULL when done, because
  the caller is always about to free(this).

- Don't reset other fields that are in a block of memory about to be free()'d.

- Implementations all now free things like internal mix buffers last, after
  closing devices and such, to guarantee they definitely aren't in use anymore
  at the point of deallocation.

src/audio/psp/SDL_pspaudio.c

@@ -126,14 +126,11 @@ static void PSPAUD_CloseDevice(_THIS)
 {
     if (this->hidden->channel >= 0) {
         sceAudioChRelease(this->hidden->channel);
-        this->hidden->channel = -1;
-    }
-
-    if (this->hidden->rawbuf != NULL) {
-        free(this->hidden->rawbuf);
-        this->hidden->rawbuf = NULL;
     }
+    free(this->hidden->rawbuf);  /* this uses memalign(), not SDL_malloc(). */
+    SDL_free(this->hidden);
 }
+
 static void PSPAUD_ThreadInit(_THIS)
 {
     /* Increase the priority of this audio thread by 1 to put it
@@ -151,7 +148,6 @@ static void PSPAUD_ThreadInit(_THIS)
 static int
 PSPAUD_Init(SDL_AudioDriverImpl * impl)
 {
-
     /* Set the function pointers */
     impl->OpenDevice = PSPAUD_OpenDevice;
     impl->PlayDevice = PSPAUD_PlayDevice;