usb_ifnum_to_if
struct usb_interface *usb_ifnum_to_if(struct usb_device *dev, uint8_t iface_no);
sc->sc_ui = usb_ifnum_to_if(uaa->device, uaa->info.bIfaceNum);
struct usb_interface *p_ui = usb_ifnum_to_if(dev, iface_no);