target: Do not return 0 from aptpl and alua configfs store functions

Here are some more instances where we are returning 0 from a configfs
store function, the unintended result of which is likely infinite retries
from userspace.

Signed-off-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>