netfilter: nft_set_pipapo_avx2: Drop the comment regarding protection

The comment claims that the kernel_fpu_begin_mask() below protects
access to the scratch map. This is not true because the access is only
protected by local_bh_disable() above.

Remove the misleading comment.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Florian Westphal <fw@strlen.de>