net: Fix warning fallout from recent NAPI interface changes.

When we removed the network device argument from several
NAPI interfaces in 908a7a16b8
("net: Remove unused netdev arg from some NAPI interfaces.")
several drivers now started getting unused variable warnings.

This fixes those up.

Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ixgb/ixgb_main.c

@@ -1742,7 +1742,6 @@ static int
 ixgb_clean(struct napi_struct *napi, int budget)
 {
 	struct ixgb_adapter *adapter = container_of(napi, struct ixgb_adapter, napi);
-	struct net_device *netdev = adapter->netdev;
 	int work_done = 0;
 
 	ixgb_clean_tx_irq(adapter);