dm verity: remove WQ_CPU_INTENSIVE flag since using WQ_UNBOUND

The documentation [1] says that WQ_CPU_INTENSIVE is "meaningless" for
unbound wq. So remove WQ_CPU_INTENSIVE from the verify_wq allocation.

1. https://www.kernel.org/doc/html/latest/core-api/workqueue.html#flags



Suggested-by: Maksym Planeta <mplaneta@os.inf.tu-dresden.de>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>