mailbox: imx: Use device-managed registration API

Get rid of some boilerplate driver removal code by using the newly added
device-managed registration API.

Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/imx-mailbox.c

@@ -324,14 +324,13 @@ static int imx_mu_probe(struct platform_device *pdev)
 
 	imx_mu_init_generic(priv);
 
-	return mbox_controller_register(&priv->mbox);
+	return devm_mbox_controller_register(dev, &priv->mbox);
 }
 
 static int imx_mu_remove(struct platform_device *pdev)
 {
 	struct imx_mu_priv *priv = platform_get_drvdata(pdev);
 
-	mbox_controller_unregister(&priv->mbox);
 	clk_disable_unprepare(priv->clk);
 
 	return 0;