Search for a disconnect ccw_device on the ccw bus rather than on the css
bus (was a typo in patch I did for the klist conversion).  A cast to an
embedding ccw_device from an embedded device in a struct subchannel will
lead us to oopses.

Signed-off-by: Cornelia Huck <cohuck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>