Wrong USBCompositeSerial::flush() realisation

[Allexin]

void USBCompositeSerial::flush(void)
{
/*Roger Clark. Rather slow method. Need to improve this */
    uint8 b;
    while(composite_cdcacm_data_available())
    {
        this->read(&b, 1);
    }
    return;
}

flush - must wait while TX channel is not empty. But here we simple wipe out all data from RX channel.