ALSA: hda/realtek - Make path->idx[] and path->multi[] consistent

So far, idx[i] and multi[i] indicate the attribute of the widget
path[i - 1].  This was just for simplifying the code in
__parse_output_path(), but this is rather confusing for later use.
It's more natural if both idx[i] and multi[i] point to the same widget
of path[i].  This patch changes to that way.

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