staging: comedi: adl_pci9118: tidy up digital input subdevice init

For aesthetics, add some whitespace to the digital input subdevice init.

Remove the SDF_GROUND and SDF_COMMON subdev_flags. These flags only apply
to analog subdevices.

Remove the 'len_chanlist' init, this subdevice member is only used with
subdevices that support async commands.

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>