sky2: Fix checksum endianness

sky2: Fix checksum endianness

sky2 driver on PowerPC targets floods kernel log with following errors:

  eth1: hw csum failure.
  Call Trace:
  [ef84b8a0] [c00075e4] show_stack+0x50/0x160 (unreliable)
  [ef84b8d0] [c02fa178] netdev_rx_csum_fault+0x3c/0x5c
  [ef84b8f0] [c02f6920] __skb_checksum_complete_head+0x7c/0x84
  [ef84b900] [c02f693c] __skb_checksum_complete+0x14/0x24
  [ef84b910] [c0337e08] tcp_v4_rcv+0x4c8/0x6f8
  [ef84b940] [c031a9c8] ip_local_deliver+0x98/0x210
  [ef84b960] [c031a788] ip_rcv+0x38c/0x534
  [ef84b990] [c0300338] netif_receive_skb+0x260/0x36c
  [ef84b9c0] [c025de00] sky2_poll+0x5dc/0xcf8
  [ef84ba20] [c02fb7fc] net_rx_action+0xc0/0x144

The NIC is Yukon-2 EC chip revision 1.

Converting checksum field from le16 to CPU byte order fixes the issue.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>