You don't need any external diodes because that H-bridge chip (like all mosfet H-bridge chips I know of) has them built in. If the current rating of the motor were a lot higher then there might be some advantage in using external Schottky diodes (to reduce power dissipation in the chip), but for 500mA I really don't think it's worthwhile. But if you do want to use external diodes, then that Schottky bridge rectifier looks OK.