drm/i915/hdmi: check port in ibx_infoframe_enabled

Add port check for ibx similar to vlv in

commit 535afa2e
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Wed Apr 15 16:52:29 2015 -0700

    drm/i915/vlv: check port in infoframe_enabled v2

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>