baresip: use return in init script

baresip: use return in init script

"start_service()" is a function, hence "return" should be used instead
of "exit".

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>
(cherry picked from commit b69ae7b9344228e1e83aaee2f62cebbd599c1388)
Signed-off-by: Richard Muzik <richard.muzik@nic.cz>