HID: wiimote: move queue handling into separate struct

The output queue is independent of the other wiimote modules and can run
on its own. Therefore, move its members into a separate struct so we don't
run into name collisions with other modules.

This is only a syntactic change that renames all queue members to queue.*.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>