Input: wm97xx - remove deprecated create_singletheread_workqueue

alloc_ordered_workqueue() replaces deprecated
create_singlethread_workqueue().

It queues work items via &wm->ts_reader and &wm->pen_event_work which map
to wm97xx_pen_irq_worker (handles a pen down interrupt) and
wm97xx_ts_reader (the touchscreen sample reader) respectively. Hence, an
ordered dedicated workqueue has been used.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>