netfilter: arp_tables: remove redundant check on ret being non-zero

ret is initialized to zero and if it is set to non-zero in the
xt_entry_foreach loop then we exit via the out_free label. Hence
the check for ret being non-zero is redundant and can be removed.

Detected by CoverityScan, CID#1357132 ("Logically Dead Code")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>