net: bcmgenet: Fix a resource leak in an error handling path in the probe functin

If the 'register_netdev()' call fails, we must undo a previous
'bcmgenet_mii_init()' call.

Fixes: 1c1008c7 ("net: bcmgenet: add main driver file")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20201212182005.120437-1-christophe.jaillet@wanadoo.frSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/broadcom/genet/bcmgenet.c

@@ -4069,8 +4069,10 @@ static int bcmgenet_probe(struct platform_device *pdev)
 	clk_disable_unprepare(priv->clk);
 
 	err = register_netdev(dev);
-	if (err)
+	if (err) {
+		bcmgenet_mii_exit(dev);
 		goto err;
+	}
 
 	return err;