Some VIA chipsets will reset the DEV bit after IEN changes on ctl. Our
optimised write path avoids doing this but we need to remove the
optimisation on these devices.

[Identified and some original patches proposed by Josehn Chan @ VIA but
discussion then all ground to a halt so given a test case I dug it back out]

Signed-off-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Tested-by: Christoph Bisping (bug #13086)
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>