staging: comedi: cb_pcidas: tidy up 8800 caldac calibration subdevice

For aesthetics, add some whitespace to the subdevice init.

It's not possible to actually read from the caldac. For convienence
the subdevice readback provided by the core is used to return the
last value written to the subdevice. Remove the SDF_READABLE flag
from the subdev_flags.

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>