Check if there is only one vendor-specific interface

 bcm20795.py

@@ -86,8 +86,9 @@
        bcm_interface = None
        for interface in configuration:
            if interface.bInterfaceClass == 0xff and interface.iInterface == 0x08:
                if bcm_interface is not None:
                    raise Exception('More than one vendor-specific interface found!')
                bcm_interface = interface
                break
        if bcm_interface is None:
            raise Exception('Cannot find vendor-specific interface')
        logger.debug('Interface found: {}'.format(bcm_interface._str()))