Returns the grizzly's internal address value. Returns a negative error value in case of error.

def get_device_address(usb_device):
        """ Returns the grizzly's internal address value. Returns a negative error value in case of error. """
        try:
            usb_device.ctrl_transfer(0x21, 0x09, 0x0300, 0, GrizzlyUSB.COMMAND_GET_ADDR)
            internal_addr = usb_device.ctrl_transfer(0xa1, 0x01, 0x0301, 0, 2)[1]
            return internal_addr >> 1
        except usb.USBError as e:
            return GrizzlyUSB.USB_DEVICE_ERROR