There's a bad hang where the driver locks the system solid trying to do
domain validation with certain devices.  The one I've managed to
reproduce it with is a Quantum Atlas.

What happens is that setting the offset to zero is an async negotiation
message.  However, the driver still seems to have DT set (which is
illegal).  Most devices just reject this as stupid, but the Quantum
seems to try to obey it and hangs the bus.

The simple fix is to reset all PPR options when the offset is set to
zero.
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>