ALSA: hda/hdmi - Fix i915 reverse port/pin mapping

The recent fix for Icelake HDMI codec introduced the mapping from pin
NID to the i915 gfx port number.  However, it forgot the reverse
mapping from the port number to the pin NID that is used in the ELD
notifier callback.  As a result, it's processed to a wrong widget and
gives a warning like
  snd_hda_codec_hdmi hdaudioC0D2: HDMI: pin nid 5 not registered

This patch corrects it with a proper reverse mapping function.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204133


Fixes: b0d8bc50 ("ALSA: hda: hdmi - add Icelake support")
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>