hwmon: (jc42) Allow negative hysteresis temperatures

The driver supports negative high and critical limits, it can return
negative hysteresis values, so there is no good reason to not let the
user write negative hysteresis values.

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