drm/i915: Clean up PPS code calling conventions

No need to pass 'dev' or 'dev_priv' when the function already takes
'intel_dp'. Also let's prefer passing 'dev_priv' instead of 'dev'
when we have to pass one or the other.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171031205123.13123-10-ville.syrjala@linux.intel.comAcked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>