From: Zhang Qiang <qiang.zhang@xxxxxxxxxxxxx>
Add a missing spinlock protection for play_queue, because
the play_queue may be destroyed when the "playback_work"
work func and "f_audio_out_ep_complete" callback func
operate this paly_queue at the same time.
Cc: stable <stable@xxxxxxxxxxxxxxx>[...]
Signed-off-by: Zhang Qiang <qiang.zhang@xxxxxxxxxxxxx>