HID: wacom: use one work queue per task

Looks like the battery hijacked the wireless worker. That's not fair so
use a work queue per task.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>