staging: comedi: cb_pcidas: tidy up calibration trimpot subdevice

For aesthetics, add some whitespace to the subdevice init.

It's not possible to actually read from the trimpot. 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.

Move the comment about the channels from trimpot_8402_write() to
the subdevice init and fix the checkpatch.pl issue about:

WARNING: Block comments use a trailing */ on a separate line

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>