block: replace always false argument with 'false'

A previous commit fixed up the condition for doing direct issue, but that
left the 'from_schedule' argument dead inside the branch. Replace it with
'false'.

Fixes: ff155223 ("blk-mq: don't issue request directly in case that current is to be blocked")
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>