fs: dlm: use alloc_ordered_workqueue

The proper way to allocate ordered workqueues is to use
alloc_ordered_workqueue() function. The current way implies an ordered
workqueue which is also required by dlm.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>