of: add EXPORT_SYMBOL for of_graph_get_endpoint_by_regs

This symbol came via exynos-next, but modular builds are broken
so just fix it up now.

Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/of/base.c

@@ -2264,6 +2264,7 @@ struct device_node *of_graph_get_endpoint_by_regs(
 
 	return NULL;
 }
+EXPORT_SYMBOL(of_graph_get_endpoint_by_regs);
 
 /**
  * of_graph_get_remote_port_parent() - get remote port's parent node