netdevice lance: Convert directly reference of netdev->priv

This patch is to kill directly reference of netdev->priv too.
Because the private data should be allocated in DMA area, alloc_etherdev()
can't satisfy this needs.
Use netdev->ml_priv to point to lance_private.

Signed-off-by: Wang Chen <wangchen@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>