Upstream-commit-id: 24e8fc49

The power_mutex lock in snd_pcm_drop may cause a possible deadlock
chain, and above all, it's unneeded.  Let's get rid of it.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>