copying /sys causes fans to spin up

[Benjamin Herrenschmidt]

> windfarm: failed to attach ds1775 hd-temp to i2c
> windfarm: failed to attach MAX6690 sensor
> 
> 
> Maybe thats harmless, but I have seen it on a few different G5.

Hrm... the windfarm sensors are useless on those old G5s that use
therm_pm72... though I wouldn't have expected them to cause harm.

Might be useful for now to make them not load on PowerMac7,2 7,3 and
RackMac3,1 tho...

Ben.