hwmon: (max6697) Fix underflow when writing limit attributes

Using DIV_ROUND_CLOSEST() on an unbound value can result in underflows.
Indeed, module test scripts report:

temp1_max: Suspected underflow: [min=0, read 255000, written -9223372036854775808]
temp1_crit: Suspected underflow: [min=0, read 255000, written -9223372036854775808]

Fix by introducing an extra set of clamping.

Fixes: 5372d2d7 ("hwmon: Driver for Maxim MAX6697 and compatibles")
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/max6697.c

@@ -311,6 +311,7 @@ static ssize_t temp_store(struct device *dev,
 		return ret;
 
 	mutex_lock(&data->update_lock);
+	temp = clamp_val(temp, -1000000, 1000000);	/* prevent underflow */
 	temp = DIV_ROUND_CLOSEST(temp, 1000) + data->temp_offset;
 	temp = clamp_val(temp, 0, data->type == max6581 ? 255 : 127);
 	data->temp[nr][index] = temp;