mailbox: use error ret code of of_parse_phandle_with_args()

In case of error, of_parse_phandle_with_args() returns -EINVAL when the
passed index is negative, or -ENOENT when the index is for an empty
phandle. The mailbox core overwrote the error return code with a less
precise -ENODEV. Use the error returned code from
of_parse_phandle_with_args().

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

Author: ambarus

drivers/mailbox/mailbox.c

@@ -415,11 +415,12 @@ struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index)
 
 	mutex_lock(&con_mutex);
 
-	if (of_parse_phandle_with_args(dev->of_node, "mboxes",
-				       "#mbox-cells", index, &spec)) {
+	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(-ENODEV);
+		return ERR_PTR(ret);
 	}
 
 	chan = ERR_PTR(-EPROBE_DEFER);