target: fix unused shift in core_scsi3_pri_report_capabilities

Clearly a right-shift was meant.  Effectively doesn't make a difference,
as add_len is hard-coded to 8 and the high byte will be zero no matter
which way you shift.  But I hate leaving bad examples for others to
copy.

Found by coverity.

Signed-off-by: Joern Engel <joern@logfs.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>