staging: comedi: comedi_fops.c: Tweak kernel-doc for consistency

Adjust the kernel-doc in this file for consistency of capitalization and
punctuation.  Make more use of the special kernel-doc markers for
parameter names, constant names, etc.  Use the correct kernel-doc tag
for the return values sections.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>