hwmon: (w83791d) Fix vrm write operation

vrm is an u8, so the written value needs to be limited to [0, 255].
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/w83791d.c

@@ -1181,6 +1181,9 @@ static ssize_t store_vrm_reg(struct device *dev,
 	if (err)
 		return err;
 
+	if (val > 255)
+		return -EINVAL;
+
 	data->vrm = val;
 	return count;
 }