staging: comedi: das1800: fix comments in das1800_ai_handler()

Fix the checkpatch.pl issues:
WARNING: line over 80 characters

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>