target: use 'se_dev_entry' when allocating UAs

We need to use 'se_dev_entry' as argument when allocating
UAs, otherwise we'll never see any UAs for an implicit
ALUA state transition triggered from userspace.

(Add target_ua_allocate_lun() common caller - nab)

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>