6lowpan: iphc: remove check on null

This memory is placed on stack and can't be null so remove the check on
null.
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/6lowpan/iphc.c

@@ -268,9 +268,6 @@ uncompress_udp_header(struct sk_buff *skb, struct udphdr *uh)
 	bool fail;
 	u8 tmp = 0, val = 0;
 
-	if (!uh)
-		goto err;
-
 	fail = lowpan_fetch_skb(skb, &tmp, sizeof(tmp));
 
 	if ((tmp & LOWPAN_NHC_UDP_MASK) == LOWPAN_NHC_UDP_ID) {