drm/nv50: fix some not-error error messages

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nv50_display.c b/drivers/gpu/drm/nouveau/nv50_display.c
index 0ab8687..f13ad0d 100644
--- a/drivers/gpu/drm/nouveau/nv50_display.c
+++ b/drivers/gpu/drm/nouveau/nv50_display.c
@@ -380,6 +380,9 @@
 	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
 		struct nouveau_connector *conn = nouveau_connector(connector);
 
+		if (conn->dcb->gpio_tag == 0xff)
+			continue;
+
 		pgpio->irq_enable(dev, conn->dcb->gpio_tag, true);
 	}