hwmon/w83627ehf: Enable VBAT monitoring

If VBAT monitoring is disabled, enable it. Original patch from
an anonymous contributor on the lm-sensors trac system:
http://lm-sensors.org/ticket/2218

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>