netfilter: nft_set_pipapo: remove scratch_aligned pointer

use ->scratch for both avx2 and the generic implementation.

After previous change the scratch->map member is always aligned properly
for AVX2, so we can just use scratch->map in AVX2 too.

The alignoff delta is stored in the scratchpad so we can reconstruct
the correct address to free the area again.

Fixes: 7400b063

 ("nft_set_pipapo: Introduce AVX2-based lookup implementation")
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>