drm/i915/dp: don't call the link parameters sink parameters

If we modify these on the fly depending on the link conditions, don't
pretend they are sink properties.

Some link vs. sink confusion still remains, but we'll take care of them
in follow-up patches.

Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/3739b4fac502ebd1c6e075a62c1a195e4094eb16.1491485983.git.jani.nikula@intel.com