staging: unisys: Clean up kthread usage

Remove the has_stopped completion as theres already one available
internally.

Correct the while loops

Remove the while loop in drain_queue as it already exists in the top level
loop

Signed-off-by: Neil Horman <nhorman@redhat.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>