staging: comedi: usbduxsigma: change private data flags to bit fields

Change the type of all the true/false flags in the private data to
bit fields.

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>