After commit:

923218f6 ("blk-mq: don't allocate driver tag upfront for flush rq")

we no longer use the 'can_block' argument in
blk_mq_sched_insert_request(). Kill it.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

Added actual commit message as to why it's being removed.
Signed-off-by: Jens Axboe <axboe@kernel.dk>