staging: comedi: usbdux: make private data flags bit-fields

Change the flags in the private data to bit-fields to save a bit of
space.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>