As PCM core handles the multiple linked streams in parallel, lockdep
gets confused (partly because of weak annotations) and spews the
false-positive warnings.  This hasn't been a problem for long time but
the latest PCM lock path update seems to have woken up a sleeping
dog.

Here is an attempt to paper over this issue: pass the lock subclass
just calculated from the depth in snd_pcm_action_group().  Also, a
(possibly) wrong lock subclass set in snd_pcm_action_lock_mutex() is
dropped, too.

Reported-and-tested-by: Arthur Marsh <arthur.marsh@internode.on.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>