s390/cio: fix kernel-doc usage

Fix the kernel-doc usage in cio to get rid of (W=1) build warnings like:
drivers/s390/cio/cio.c:1068: warning: No description found for parameter 'sch'

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>