target: Fix WRITE_SAME_16 lba assignment breakage

This patch fixes a bug in WRITE_SAME_16 LBA assignment where get_unaligned_be16()
is incorrectly being used instead of get_unaligned_be64() for a 64-bit LBA.

This was introduced with:

commit a1d8b49a
Author: Andy Grover <agrover@redhat.com>
Date:   Mon May 2 17:12:10 2011 -0700

    target: Updates from AGrover and HCH (round 3)

    (target: inline struct se_transport_task into struct se_cmd)

Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>