ASoC: handle mutex correctly to avoid possible deadlock

Unlock mutex in stream->device to avoid a possible deadlock
when returned from function snd_compr_drain() in error case
without unlocking the mutex.

Change-Id: I24a5af4e2eaa5fd636a6c1b1afb461bfd461617f
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>