drm/i915: Restore planes after load detection

Actually turn the planes back on after were done with
the load detection.

Fixes: 20bdc112 ("drm/i915: Disable all planes for load detection, v2.")
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180322152313.6561-23-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -9974,6 +9974,8 @@ int intel_get_load_detect_pipe(struct drm_connector *connector,
 	ret = PTR_ERR_OR_ZERO(drm_atomic_get_connector_state(restore_state, connector));
 	if (!ret)
 		ret = PTR_ERR_OR_ZERO(drm_atomic_get_crtc_state(restore_state, crtc));
+	if (!ret)
+		ret = drm_atomic_add_affected_planes(restore_state, crtc);
 	if (ret) {
 		DRM_DEBUG_KMS("Failed to create a copy of old state to restore: %i\n", ret);
 		goto fail;