ems_usb: cleanup: remove uneeded check

"skb" is alway non-null here, but even if it were null the check isn't
needed because dev_kfree_skb() can handle it.

This eliminates a smatch warning about dereferencing a variable before
checking that it is non-null.
Signed-off-by: NDan Carpenter <error27@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/can/usb/ems_usb.c

@@ -876,9 +876,7 @@ static netdev_tx_t ems_usb_start_xmit(struct sk_buff *skb, struct net_device *ne
 	return NETDEV_TX_OK;
 
 nomem:
-	if (skb)
-		dev_kfree_skb(skb);
-
+	dev_kfree_skb(skb);
 	stats->tx_dropped++;
 
 	return NETDEV_TX_OK;