drm/i915: Remove the double register write from intel_disable_hdmi()

IBX can have problems with the first write to the port register getting
masked when enabling the port. We are trying to apply the workaround
also when disabling the port where it's not needed, and we also try
to apply it for CPT/PPT as well which don't need it. Just kill it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[danvet: Resolve conflict with the remove CHV if block.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>