libretro: update av info in deferred setup

Not sure this is entirely necessary but throwing it in out of an
abundance of caution. Doesn't seem to hurt anything.

src/platform/libretro/libretro.c

@@ -1271,6 +1271,7 @@ static void _doDeferredSetup(void) {
 		save->close(save);
 	}
 	stream.audioRateChanged = _audioRateChanged;
+    _audioRateChanged(NULL, 0);
 	deferredSetup = false;
 }