scsi: target: convert boolean se_dev_attrib types to bool

This should harden us against configfs API regressions similar to the one
fixed by the previous commit.

Link: https://marc.info/?l=target-devel&m=158211731505174


Signed-off-by: David Disseldorp <ddiss@suse.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>