staging: comedi: das16m1: tidy up digital output subdevice init

Add some whitespace to the subdevice init and rename the support
function.

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>