ipv6: sr: fix useless rol32 call on hash

The rol32 call is currently rotating hash but the rol'd value is
being discarded. I believe the current code is incorrect and hash
should be assigned the rotated value returned from rol32.

Detected by CoverityScan, CID#1468411 ("Useless call")

Fixes: b5facfdb ("ipv6: sr: Compute flowlabel for outer IPv6 header of seg6 encap mode")
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Acked-by: dlebrun@google.com
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/seg6_iptunnel.c

@@ -101,7 +101,7 @@ static __be32 seg6_make_flowlabel(struct net *net, struct sk_buff *skb,
 
 	if (do_flowlabel > 0) {
 		hash = skb_get_hash(skb);
-		rol32(hash, 16);
+		hash = rol32(hash, 16);
 		flowlabel = (__force __be32)hash & IPV6_FLOWLABEL_MASK;
 	} else if (!do_flowlabel && skb->protocol == htons(ETH_P_IPV6)) {
 		flowlabel = ip6_flowlabel(inner_hdr);