dm-delay: fix hung task introduced by kthread mode

If the worker thread is not woken due to a bio, then it is not woken at
all. This causes the hung task check to trigger. This occurs, for
instance, when no bios are submitted. Also when a delay of 0 is
configured, delay_bio() returns without waking the worker.

Prevent the hung task check from triggering by creating the thread with
kthread_run() instead of using kthread_create() directly.

Fixes: 70bbeb29

 ("dm delay: for short delays, use kthread instead of timers and wq")
Signed-off-by: Joel Colledge <joel.colledge@linbit.com>
Reviewed-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>