[S390]: Adapt monreader driver to new IUCV API

Adapt monreader character device driver to new IUCV API

Signed-off-by: Frank Pavlic <fpavlic@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>