mailbox: hi6220: Use device-managed registration API

Get rid of some boilerplate driver removal code by using the newly added
device-managed registration API.
Reviewed-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/hi6220-mailbox.c

@@ -349,7 +349,7 @@ static int hi6220_mbox_probe(struct platform_device *pdev)
 		mbox->controller.txpoll_period = 5;
 	}
 
-	err = mbox_controller_register(&mbox->controller);
+	err = devm_mbox_controller_register(dev, &mbox->controller);
 	if (err) {
 		dev_err(dev, "Failed to register mailbox %d\n", err);
 		return err;
@@ -360,14 +360,6 @@ static int hi6220_mbox_probe(struct platform_device *pdev)
 	return 0;
 }
 
-static int hi6220_mbox_remove(struct platform_device *pdev)
-{
-	struct hi6220_mbox *mbox = platform_get_drvdata(pdev);
-
-	mbox_controller_unregister(&mbox->controller);
-	return 0;
-}
-
 static struct platform_driver hi6220_mbox_driver = {
 	.driver = {
 		.name = "hi6220-mbox",
@@ -375,7 +367,6 @@ static struct platform_driver hi6220_mbox_driver = {
 		.of_match_table = hi6220_mbox_of_match,
 	},
 	.probe	= hi6220_mbox_probe,
-	.remove	= hi6220_mbox_remove,
 };
 
 static int __init hi6220_mbox_init(void)