ALSA: hda - Allow concurrent RIRB access in single_cmd mode

In the single_cmd mode, the current driver code doesn't do any update
for RIRB just for any safety reason.  But, actually the RIRB and
single_cmd mode don't conflict.  Unsolicited events can be delivered
even while using the single_cmd mode.

This patch allows the handling of unsolicited events with single_cmd
mode, just always checking RIRB independent from single_cmd flag.

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