target: Fix WRITE_SAME_16 t_task_lba assignment bug

This patch fixes a bug in the assignment of cmd->t_task.t_task_lba with
WRITE_SAME_16 to correctly use get_unaligned_be64() for the 64-bit LBA.

Reported-by: Chris Greiveldinger <chris.greiveldinger@rnanetworks.com>
Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>