drm/i915/dp: Pass around intel_connector rather than drm_connector

Prefer to use intel_connector over drm_connector. Also clean
up the related variable names a bit.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220322120015.28074-7-ville.syrjala@linux.intel.com
Reviewed-by: Uma Shankar <uma.shankar@intel.com>