To keep things clear rename the intel_dp->supported_rates[] to
intel_dp->sink_rates[], and rename the supported_rates[] name we used
elsewhere for the intersection of source and sink rates to
common_rates[].

Cc: Sonika Jindal <sonika.jindal@intel.com>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NSonika Jindal <sonika.jindal@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>