hwmon: (adt7410) Clear unwanted bits in the config register

Make sure to clear the mode bits from the config register before setting the new
mode. Otherwise we might end up with a different mode than we want to.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Reviewed-by: Hartmut Knaack <knaack.h@gmx.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>