[ALSA] usb-audio - Fix race in reconnection

Fix the race at reconnection of the device.
The disconnected usb_chip[] must be cleared before the next probe
call properly.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/usbaudio.c

@@ -3424,7 +3424,6 @@ static void snd_usb_audio_create_proc(struct snd_usb_audio *chip)
 
 static int snd_usb_audio_free(struct snd_usb_audio *chip)
 {
-	usb_chip[chip->index] = NULL;
 	kfree(chip);
 	return 0;
 }
@@ -3689,6 +3688,7 @@ static void snd_usb_audio_disconnect(struct usb_device *dev, void *ptr)
 		list_for_each(p, &chip->mixer_list) {
 			snd_usb_mixer_disconnect(p);
 		}
+		usb_chip[chip->index] = NULL;
 		mutex_unlock(&register_mutex);
 		snd_card_free_when_closed(card);
 	} else {