mISDN: remove redundant null pointer check before kfree_skb

kfree_skb has taken the null pointer into account. hence it is safe
to remove the redundant null pointer check before kfree_skb.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/mISDN/socket.c

@@ -236,8 +236,7 @@ mISDN_sock_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
 	}
 
 done:
-	if (skb)
-		kfree_skb(skb);
+	kfree_skb(skb);
 	release_sock(sk);
 	return err;
 }