hwmon: (jc42) Fix integer overflow when writing hysteresis value

Subtracting an unsigned long from a signed value causes an overflow with large
values. Use clamp_val() to reduce the number range prior to subtracting it
from the temperature limit.

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