netdevice hamradio: Convert directly reference of netdev->priv

Since all the memory, which pointed by netdev->priv, are allocated in
advance instead of by alloc_netdev().  Use netdev->ml_priv to point to
those memory.

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