staging: comedi: das16: change type of private data 'timer_running'

This member of the private data is a true/false flag. For aesthetics,
change the type to an unsigned int bit-field to save a bit of space.

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