ALSA: mixart, fix lock imbalance

There is an omitted unlock in one snd_mixart_hw_params fail path. Fix it.
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/mixart/mixart.c

@@ -607,6 +607,7 @@ static int snd_mixart_hw_params(struct snd_pcm_substream *subs,
 	/* set the format to the board */
 	err = mixart_set_format(stream, format);
 	if(err < 0) {
+		mutex_unlock(&mgr->setup_mutex);
 		return err;
 	}