The device lm90 can be controlled by the vcc rail.
Adding the regulator support to power on/off the vcc rail.
Enable the "vcc" regulator before accessing the device.
[JD: Rename variables to avoid confusion with registers.]
Signed-off-by: Wei Ni <wni@nvidia.com> Signed-off-by: Jean Delvare <khali@linux-fr.org>