cxgb4: remove cast when saving IPv4 partial checksum

The checksum field in IPv4 header is in __sum16 and ip_fast_csum()
also returns __sum16. So, no need to cast it to u16.

Fixes following sparse warning:
sge.c:1539:47: warning: cast from restricted __sum16
sge.c:1539:44: warning: incorrect type in assignment (different base types)
sge.c:1539:44:    expected restricted __sum16 [usertype] check
sge.c:1539:44:    got unsigned short [usertype]

Fixes: d0a1299c ("cxgb4: add support for vxlan segmentation offload")
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb4/sge.c

@@ -1524,8 +1524,7 @@ static netdev_tx_t cxgb4_eth_xmit(struct sk_buff *skb, struct net_device *dev)
 			if (iph->version == 4) {
 				iph->check = 0;
 				iph->tot_len = 0;
-				iph->check = (u16)(~ip_fast_csum((u8 *)iph,
-								 iph->ihl));
+				iph->check = ~ip_fast_csum((u8 *)iph, iph->ihl);
 			}
 			if (skb->ip_summed == CHECKSUM_PARTIAL)
 				cntrl = hwcsum(adap->params.chip, skb);