drm/i915: Fix new_config and new_enabled for load detect

I forgot to set new_config and new_enabled appropriately in the load
detect code. Fix it up.

v2: Handle the other error path in intel_get_load_detect_pipe() too (Imre)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>