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: Colin Ian King <colin.king@canonical.com>
Acked-by:  <dlebrun@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>