cfq-iosched: apply bool value where we return 0/1

cfq-iosched: apply bool value where we return 0/1

Saves 16 bytes of text, woohoo. But the more important point is
that it makes the code more readable when returning bool for 0/1
cases.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>