serial: pmac_zilog: use for_each_child_of_node() macro

Use for_each_child_of_node() macro instead of open coding it.
Signed-off-by: Qinglang Miao <miaoqinglang@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200916062138.191188-1-miaoqinglang@huawei.com

drivers/tty/serial/pmac_zilog.c

@@ -1644,7 +1644,7 @@ static int __init pmz_probe(void)
 		 * TODO: Add routines with proper locking to do that...
 		 */
 		node_a = node_b = NULL;
-		for (np = NULL; (np = of_get_next_child(node_p, np)) != NULL;) {
+		for_each_child_of_node(node_p, np) {
 			if (of_node_name_prefix(np, "ch-a"))
 				node_a = of_node_get(np);
 			else if (of_node_name_prefix(np, "ch-b"))