[ALSA] hda-intel - Fix Oops with ATI HDMI devices

The driver gets Oops with ATI HDMI devices due to the wrong calculation
of index for playback streams.  This patch fixes it.  Reference:
	https://bugtrack.alsa-project.org/alsa-bug/view.php?id=3746

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>