pcm: direct: Fix deadlock in poll_descriptors

pcm: direct: Fix deadlock in poll_descriptors

The recent change in PCM direct plugins to check XRUN in
poll_descriptors callback caused a regression; as consequence, the
whole playback hangs up.

The culprit is a mutex dead lock by the call in snd_pcm_state() inside
the new snd_pcm_direct_poll_descriptors().  The poll_descriptors code
path is protected with pcm mutex, thus an unlocked version
(__snd_pcm_state()) has to be used inside the callback instead.

Fixes: 789ee39727a1 ("pcm: direct: check state before enter poll on timer")
Signed-off-by: Takashi Iwai <tiwai@suse.de>