tls: Fix copy-paste error in tls_device_reencrypt

It seems that the proper structure to use in this particular
case is *skb_iter* instead of skb.

Addresses-Coverity-ID: 1471906 ("Copy-paste error")
Fixes: 4799ac81 ("tls: Add rx inline crypto offload")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>