ALSA: firewire-motu: fix double unlocked 'motu->mutex'

Mutex is doubly unlocked in some error path of pcm.open. This commit fixes
ALSA firewire-motu driver in Linux kernel v5.5.

Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 3fd80b2 ("ALSA: firewire-motu: use the same size of period for PCM substream in AMDTP streams")
Fixes: 0f5482e ("ALSA: firewire-motu: share PCM buffer size for both direction")
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20191208232226.6685-1-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/motu/motu-pcm.c

@@ -177,18 +177,14 @@ static int pcm_open(struct snd_pcm_substream *substream)
  err = snd_pcm_hw_constraint_minmax(substream->runtime,
  SNDRV_PCM_HW_PARAM_PERIOD_SIZE,
  frames_per_period, frames_per_period);
- if (err < 0) {
- mutex_unlock(&motu->mutex);
+ if (err < 0)
  goto err_locked;
- }
 
  err = snd_pcm_hw_constraint_minmax(substream->runtime,
  SNDRV_PCM_HW_PARAM_BUFFER_SIZE,
  frames_per_buffer, frames_per_buffer);
- if (err < 0) {
- mutex_unlock(&motu->mutex);
+ if (err < 0)
  goto err_locked;
- }
  }
  }