The port_mst_index parameter was reserved for future use, but
maintainers prefer to add it later when it is actually used.

[Note: this is an update patch to commit [51e1d83c: drm/i915: Call
 audio pin/ELD notify function] where I mistakenly applied the older
 version.  Jani and Daniel's review tags were to the latest version,
 so I add them below, too -- tiwai]
Signed-off-by: NDavid Henningsson <david.henningsson@canonical.com>
Reviewed-by: NJani Nikula <jani.nikula@intel.com>
Acked-by: NDaniel Vetter <daniel@ffwll.ch>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>