netfilter: ipset: Compress return logic

Simplify function returns by merging assignment and return into one
command line.

Signed-off-by: simran singhal <singhalsimran0@gmail.com>
Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>