hwmon: (lm87) Fix vrm write operation

vrm is an u8, so the written value needs to be limited to [0, 255].

Signed-off-by: Axel Lin <[e-mail]>
Signed-off-by: Guenter Roeck <[e-mail]>

drivers/hwmon/lm87.c

···
 	err = kstrtoul(buf, 10, &val);
 	if (err)
 		return err;
+
+	if (val > 255)
+		return -EINVAL;
+
 	data->vrm = val;
 	return count;
 }