drivers: net: declance: fix comparing pointer to 0

Fixes coccicheck warning:

./drivers/net/ethernet/amd/declance.c:611:14-15:
	WARNING comparing pointer to 0

Replace "skb == 0" with "!skb".
Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/amd/declance.c

@@ -608,7 +608,7 @@ static int lance_rx(struct net_device *dev)
 			len = (*rds_ptr(rd, mblength, lp->type) & 0xfff) - 4;
 			skb = netdev_alloc_skb(dev, len + 2);
 
-			if (skb == 0) {
+			if (!skb) {
 				dev->stats.rx_dropped++;
 				*rds_ptr(rd, mblength, lp->type) = 0;
 				*rds_ptr(rd, rmd1, lp->type) =