sunbmac: remove unnecessary setting of skb->dev

skb->dev is being unnecessarily set during ring init and skb alloc in rx.  It is
already being set to the proper value when eth_type_trans is called on packet
receive, and the skb->dev is not referenced anywhere else in the code.

Signed-off-by: Jon Mason <jdmason@kudzu.us>
Signed-off-by: David S. Miller <davem@davemloft.net>