drm/i915: Favor last VBT child device with conflicting AUX ch/DDC pin

The first come first served apporoach to handling the VBT
child device AUX ch conflicts has backfired. We have machines
in the wild where the VBT specifies both port A eDP and
port E DP (in that order) with port E being the real one.

So let's try to flip the preference around and let the last
child device win once again.

Cc: stable@vger.kernel.org
Cc: Jani Nikula <jani.nikula@intel.com>
Tested-by: Masami Ichikawa <masami256@gmail.com>
Tested-by: Torsten <freedesktop201910@liggy.de>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111966
Fixes: 36a0f920

 ("drm/i915/bios: make child device order the priority order")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191011202030.8829-1-ville.syrjala@linux.intel.com
Acked-by: Jani Nikula <jani.nikula@intel.com>