[SCSI] target: Fix volume size misreporting for volumes > 2TB

the target infrastructure fails to send the correct conventional size
to READ_CAPACITY that force a retry with READ_CAPACITY_16, which reads
the capacity for devices > 2TB.  Fix by adding the correct return to
trigger RC(16).

Reported-by: Ben Jarvis <bjarvismn@gmail.com>
Signed-off-by: Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>
Cc: stable@kernel.org
Signed-off-by: James Bottomley <James.Bottomley@suse.de>