mailbox: mtk: add missing of_node_put before return

Fix following coccicheck warning:
WARNING: Function "for_each_child_of_node"
should have of_node_put() before return.

Early exits from for_each_child_of_node should decrement the
node reference counter.
Signed-off-by: NWang Qing <wangqing@vivo.com>
Signed-off-by: NJassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/mtk-cmdq-mailbox.c

@@ -573,6 +573,7 @@ static int cmdq_probe(struct platform_device *pdev)
 				cmdq->clocks[alias_id].id = clk_names[alias_id];
 				cmdq->clocks[alias_id].clk = of_clk_get(node, 0);
 				if (IS_ERR(cmdq->clocks[alias_id].clk)) {
+					of_node_put(node);
 					return dev_err_probe(dev,
 							     PTR_ERR(cmdq->clocks[alias_id].clk),
 							     "failed to get gce clk: %d\n",