hwmon: (adt7470) Fix overflows seen when writing into limit attributes

Fix overflows seen when writing large values into various temperature limit
attributes.

The input value passed to DIV_ROUND_CLOSEST() needs to be clamped to avoid
such overflows.

Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>