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: 1c1008c793fa ("net: bcmgenet: add main driver file")
Signed-off-by: Christophe JAILLET <[e-mail]>
Acked-by: Florian Fainelli <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

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

···
 	clk_disable_unprepare(priv->clk);
 
 	err = register_netdev(dev);
-	if (err)
+	if (err) {
+		bcmgenet_mii_exit(dev);
 		goto err;
+	}
 
 	return err;