Regulators: wm831x-xxx - clean up driver data after removal

It is a good tone to reset driver data after unbinding the device.
Also set up drivers owner.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>