usbFindDevice():get usb device according to
                idVendor, idProduct, bus, device
                it is the exact match of the four parameters

usbFindDeviceByBus():get usb device according to bus, device
                  it returns only one usb device same as usbFindDevice

usbFindDeviceByVendor():get usb device according to idVendor,idProduct
                     it probably returns multiple usb devices.

usbDeviceSearch(): a helper function to do the actual search