ALSA: hda/hdmi: Fix incorrect mutex unlock in silent_stream_disable()

The silent_stream_disable() function introduced by the commit
b1a50397 ("ALSA: hda/hdmi: fix silent stream for first playback to
DP") takes the per_pin->lock mutex, but it unlocks the wrong one,
spec->pcm_lock, which causes a deadlock.  This patch corrects it.

Fixes: b1a50397 ("ALSA: hda/hdmi: fix silent stream for first playback to DP")
Reported-by: Jan Alexander Steffens (heftig) <heftig@archlinux.org>
Cc: <stable@vger.kernel.org>
Acked-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Link: https://lore.kernel.org/r/20210101083852.12094-1-tiwai@suse.de


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