Staging: comedi: fix print(k) coding style issue in aio_aio12_8.c

This is a patch to the aio_aio12_8.c that fixes up print(k) warnings found by the checkpatch.pl tool

Signed-off-by: Maurice Dawson <mauricedawson2699@googlemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>