drm/i915: Correctly terminate connector iteration

One should use drm_connector_list_iter_end() rather than
drm_connector_list_iter_begin() to terminate the connector
iteration.

Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Uma Shankar <uma.shankar@intel.com>
Closes: https://gitlab.freedesktop.org/drm/intel/issues/1278
Fixes: e24bcd34

 ("drm/i915/dp: Add all tiled and port sync conns to modeset")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200221154310.14858-1-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>