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_intel.c b/sound/pci/hda/hda_intel.c
index f04de11..11e791b 100644
--- a/sound/pci/hda/hda_intel.c
+++ b/sound/pci/hda/hda_intel.c
@@ -996,10 +996,11 @@
 				spin_unlock(&chip->reg_lock);
 				snd_pcm_period_elapsed(azx_dev->substream);
 				spin_lock(&chip->reg_lock);
-			} else {
+			} else if (chip->bus && chip->bus->workq) {
 				/* bogus IRQ, process it later */
 				azx_dev->irq_pending = 1;
-				schedule_work(&chip->irq_pending_work);
+				queue_work(chip->bus->workq,
+					   &chip->irq_pending_work);
 			}
 		}
 	}
@@ -1741,7 +1742,6 @@
 	for (i = 0; i < chip->num_streams; i++)
 		chip->azx_dev[i].irq_pending = 0;
 	spin_unlock_irq(&chip->reg_lock);
-	flush_scheduled_work();
 }
 
 static struct snd_pcm_ops azx_pcm_ops = {