drm/nouveau: use drm_for_each_connector_iter()

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

Cc: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170511191049.28944-6-gustavo@padovan.org

drivers/gpu/drm/nouveau/nv50_display.c

@@ -2872,17 +2872,20 @@ nv50_msto_enable(struct drm_encoder *encoder)
 	struct nv50_mstc *mstc = NULL;
 	struct nv50_mstm *mstm = NULL;
 	struct drm_connector *connector;
+	struct drm_connector_list_iter conn_iter;
 	u8 proto, depth;
 	int slots;
 	bool r;
 
-	drm_for_each_connector(connector, encoder->dev) {
+	drm_connector_list_iter_begin(encoder->dev, &conn_iter);
+	drm_for_each_connector_iter(connector, &conn_iter) {
 		if (connector->state->best_encoder == &msto->encoder) {
 			mstc = nv50_mstc(connector);
 			mstm = mstc->mstm;
 			break;
 		}
 	}
+	drm_connector_list_iter_end(&conn_iter);
 
 	if (WARN_ON(!mstc))
 		return;