staging: comedi: icp_multi: tidy up subdevice init

For aesthetics, add some whitespace to the subdevice initialization.

Remove the unnecessary initialization of the 'len_chanlist' for each
subdevice. That member is only used by subdevices that support async
commands.

Also, remove the initialzation of the dev->read_subdev. That member
is also only used for async command support.

Rename some of the subdevice functions to follow the normal format
used in comedi drivers.

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>