ALSA: hda - Fix pending unsol events at shutdown

This is an alternative fix attemp for the issue reported in the commit
caa8422d ("ALSA: hda: Flush interrupts on disabling") that was
reverted later due to regressions.  Instead of tweaking the hardware
disablement order and the enforced irq flushing, do calling
cancel_work_sync() of the unsol work early enough, and explicitly
ignore the unsol events during the shutdown by checking the
bus->shutdown flag.

Fixes: caa8422d ("ALSA: hda: Flush interrupts on disabling")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://lore.kernel.org/r/s5h1ruxt9cz.wl-tiwai@suse.de


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