netfilter: conntrack: remote a return value of the 'seq_print_acct' function.

The static 'seq_print_acct' function always returns 0.

Change the return value to 'void' and remove unnecessary checks.

Found by InfoTeCS on behalf of Linux Verification Center
(linuxtesting.org) with SVACE.

Fixes: 1ca9e417 ("netfilter: Remove uses of seq_<foo> return values")
Signed-off-by: Ilia.Gavrilov <Ilia.Gavrilov@infotecs.ru>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>