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

drivers/hwmon/w83791d.c

···
 	if (err)
 		return err;
 
+	if (val > 255)
+		return -EINVAL;
+
 	data->vrm = val;
 	return count;
 }