netfilter: nft_set_hash: bogus element self comparison from deactivation path

Use the element from the loop iteration, not the same element we want to
deactivate otherwise this branch always evaluates true.

Fixes: 6c03ae21 ("netfilter: nft_set_hash: add non-resizable hashtable implementation")
Reported-by: Florian Westphal <fw@strlen.de>
Tested-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>