[S390] cio: css_probe_device() must be called enabled.

Move css_probe_device() behind giving up the lock for the old subchannel
in css_evaluate_known_subchannel() so we aren't disabled when we call it.

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