net: ethernet: fix potential use-after-free in ec_bhf_remove

static void ec_bhf_remove(struct pci_dev *dev)
{
...
	struct ec_bhf_priv *priv = netdev_priv(net_dev);

	unregister_netdev(net_dev);
	free_netdev(net_dev);

	pci_iounmap(dev, priv->dma_io);
	pci_iounmap(dev, priv->io);
...
}

priv is netdev private data, but it is used
after free_netdev(). It can cause use-after-free when accessing priv
pointer. So, fix it by moving free_netdev() after pci_iounmap()
calls.

Fixes: 6af55ff5 ("Driver for Beckhoff CX5020 EtherCAT master module.")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>