alx: add missing stats_lock spinlock init

Trivial fix for init time stack trace occuring in
alx_get_stats64 upon start up. Should have been part of
commit adding the spinlock:
f1b6b106 alx: add alx_get_stats64 operation
Signed-off-by: John Greene <jogreene@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/atheros/alx/main.c

@@ -1292,6 +1292,7 @@ static int alx_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 	alx = netdev_priv(netdev);
 	spin_lock_init(&alx->hw.mdio_lock);
 	spin_lock_init(&alx->irq_lock);
+	spin_lock_init(&alx->stats_lock);
 	alx->dev = netdev;
 	alx->hw.pdev = pdev;
 	alx->msg_enable = NETIF_MSG_LINK | NETIF_MSG_HW | NETIF_MSG_IFUP |