bio-integrity: fix boolreturn.cocci warnings

block/bio-integrity.c:318:10-11: WARNING: return of 0/1 in function 'bio_integrity_prep' with return type bool

 Return statements in functions returning bool should use
 true/false instead of 1/0.
Generated by: scripts/coccinelle/misc/boolreturn.cocci

Fixes: e23947bd ("bio-integrity: fold bio_integrity_enabled to bio_integrity_prep")
CC: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>