ALSA: hda - Don't handle ELD notify from invalid port

The current Intel HDMI codec driver supports only three fixed ports
from port B to port D.  However, i915 driver may assign a DP on other
ports, e.g. port A, when no eDP is used.  This incompatibility is
caught later at pin_nid_to_pin_index() and results in a warning
message like "HDMI: pin nid 4 not registered" at each time.

This patch filters out such invalid events beforehand, so that the
kernel won't be too grumbling.

Reported-by: Stefan Assmann <sassmann@kpanic.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>