staging: comedi: use help instead of ---help--- in Kconfig

  - Resolve the following warning from the Kconfig,
    "WARNING: prefer 'help' over '---help---' for new help texts"

Signed-off-by: Moses Christopher <moseschristopherb@gmail.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>