drm/atomic: Clean up update_connector_routing.

connector_state->crtc can no longer be unset by accident,
so that check can be removed. The other code open-codes
drm_atomic_get_existing_crtc_state, so use that.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[danvet: Resolve tiny conflict due to gcc warning fix on previous
patch.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_atomic_helper.c

@@ -265,7 +265,6 @@ update_connector_routing(struct drm_atomic_state *state,
 	const struct drm_connector_helper_funcs *funcs;
 	struct drm_encoder *new_encoder;
 	struct drm_crtc_state *crtc_state;
-	int idx;
 
 	DRM_DEBUG_ATOMIC("Updating routing for [CONNECTOR:%d:%s]\n",
 			 connector->base.id,
@@ -273,16 +272,12 @@ update_connector_routing(struct drm_atomic_state *state,
 
 	if (connector->state->crtc != connector_state->crtc) {
 		if (connector->state->crtc) {
-			idx = drm_crtc_index(connector->state->crtc);
-
-			crtc_state = state->crtc_states[idx];
+			crtc_state = drm_atomic_get_existing_crtc_state(state, connector->state->crtc);
 			crtc_state->connectors_changed = true;
 		}
 
 		if (connector_state->crtc) {
-			idx = drm_crtc_index(connector_state->crtc);
-
-			crtc_state = state->crtc_states[idx];
+			crtc_state = drm_atomic_get_existing_crtc_state(state, connector_state->crtc);
 			crtc_state->connectors_changed = true;
 		}
 	}
@@ -336,14 +331,9 @@ update_connector_routing(struct drm_atomic_state *state,
 
 	steal_encoder(state, new_encoder);
 
-	if (WARN_ON(!connector_state->crtc))
-		return -EINVAL;
-
 	set_best_encoder(state, connector_state, new_encoder);
 
-	idx = drm_crtc_index(connector_state->crtc);
-
-	crtc_state = state->crtc_states[idx];
+	crtc_state = drm_atomic_get_existing_crtc_state(state, connector_state->crtc);
 	crtc_state->connectors_changed = true;
 
 	DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] using [ENCODER:%d:%s] on [CRTC:%d:%s]\n",