staging: unisys: visornic: Remove create_singlethread_workqueue()

With concurrency managed workqueues, use of dedicated workqueues
can be replaced by using system_wq.
Drop visornic_timeout_reset_workqueue by using system_wq.

Since there is only one work item per devdata and different
devdatas do not need to be ordered, increase of concurrency
level by switching to system_wq should not break anything.

cancel_work_sync() is used to ensure that work is not pending or
executing on any CPU.

Signed-off-by: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Tested-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>