[S390] cio: Reorganize initialization.

- Localize more of the init calls in init_channel_subsystem().
- Print a warning if init_channel_subsystem() failed.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>