mailbox: don't protect of_parse_phandle_with_args with con_mutex

There are no concurrency problems if multiple consumers parse the
phandle, don't gratuiously protect the parsing with the mutex used
for the controllers list.

Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>

Author: ambarus

drivers/mailbox/mailbox.c

@@ -413,16 +413,15 @@ struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index)
 		return ERR_PTR(-ENODEV);
 	}
 
-	mutex_lock(&con_mutex);
-
 	ret = of_parse_phandle_with_args(dev->of_node, "mboxes", "#mbox-cells",
 					 index, &spec);
 	if (ret) {
 		dev_dbg(dev, "%s: can't parse \"mboxes\" property\n", __func__);
-		mutex_unlock(&con_mutex);
 		return ERR_PTR(ret);
 	}
 
+	mutex_lock(&con_mutex);
+
 	chan = ERR_PTR(-EPROBE_DEFER);
 	list_for_each_entry(mbox, &mbox_cons, node)
 		if (mbox->dev->of_node == spec.np) {