mailbox: handle failed named mailbox channel request

Previously, if mbox_request_channel_byname was used with a name
which did not exist in the "mbox-names" property of a mailbox
client, the mailbox corresponding to the last entry in the
"mbox-names" list would be incorrectly selected.
With this patch, -EINVAL is returned if the named mailbox is
not found.
Signed-off-by: NMorten Borup Petersen <morten_bp@live.dk>
Signed-off-by: NJassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/mailbox.c

@@ -418,11 +418,13 @@ struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,
 
 	of_property_for_each_string(np, "mbox-names", prop, mbox_name) {
 		if (!strncmp(name, mbox_name, strlen(name)))
-			break;
+			return mbox_request_channel(cl, index);
 		index++;
 	}
 
-	return mbox_request_channel(cl, index);
+	dev_err(cl->dev, "%s() could not locate channel named \"%s\"\n",
+		__func__, name);
+	return ERR_PTR(-EINVAL);
 }
 EXPORT_SYMBOL_GPL(mbox_request_channel_byname);