drm/vc4: use drm_for_each_connector_iter()

Drop legacy drm_for_each_connector() in favor of the race-free
drm_for_each_connector_iter().

v2: add missing drm_connector_list_iter_end(Daniel Vetter)

Cc: Eric Anholt <eric@anholt.net>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Eric Anholt <eric@anholt.net>
Link: http://patchwork.freedesktop.org/patch/msgid/20170512164100.7649-1-gustavo@padovan.org

drivers/gpu/drm/vc4/vc4_crtc.c

@@ -345,12 +345,16 @@ static u32 vc4_get_fifo_full_level(u32 format)
 static struct drm_encoder *vc4_get_crtc_encoder(struct drm_crtc *crtc)
 {
 	struct drm_connector *connector;
+	struct drm_connector_list_iter conn_iter;
 
-	drm_for_each_connector(connector, crtc->dev) {
+	drm_connector_list_iter_begin(crtc->dev, &conn_iter);
+	drm_for_each_connector_iter(connector, &conn_iter) {
 		if (connector->state->crtc == crtc) {
+			drm_connector_list_iter_end(&conn_iter);
 			return connector->encoder;
 		}
 	}
+	drm_connector_list_iter_end(&conn_iter);
 
 	return NULL;
 }