ALSA: hda - More relax for pending period handling

Since the pending periods are often bogus and take long time until
actually processed, it often results in a high CPU usage of the hd-audio
workq.  Overall it's better to have low CPU consumption by avoiding a
too tight loop rather than the wake-up timing accuracy.

Signed-off-by: Takashi Iwai <tiwai@suse.de>