drm/i915/chv: Fix gmbus for port D

On CHV the GMBUS port for port D is different from other gmch platforms
which have port D. Fix it up.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Antti Koskipää <antti.koskipaa@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>