usb: mtu3: implement udc_async_callbacks of gadget operation

Implement udc_async_callbacks hook function to avoid a race when unnbinding
gadget drivers, refer to:
7dc0c55e

 ('USB: UDC core: Add udc_async_callbacks gadget op')

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/20220609074233.15532-2-chunfeng.yun@mediatek.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>