ALSA: hda - Use own workqueue

snd-hda-intel driver used schedule_work() fot the delayed DMA pointer
updates, but this has several potential problems:
- it may block other eventsd works longer
- it may deadlock when probing fails and flush_scheduled_work() is
  called during probe callback (as probe callback itself could be
  invoked from eventd)

This patch adds an own workq for each driver instance to solve these
problems.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/pci/hda/hda_codec.h b/sound/pci/hda/hda_codec.h
index e9c723e..5810ef5 100644
--- a/sound/pci/hda/hda_codec.h
+++ b/sound/pci/hda/hda_codec.h
@@ -614,6 +614,7 @@
 
 	/* unsolicited event queue */
 	struct hda_bus_unsolicited *unsol;
+	struct workqueue_struct *workq;	/* common workqueue for codecs */
 
 	/* assigned PCMs */
 	DECLARE_BITMAP(pcm_dev_bits, SNDRV_PCM_DEVICES);