[S390] cio: Fix race for "fast" path gone/path back situations.

Make sure we wait for previous evaluations triggered by path state
changes to have settled before we manipulate path states again.

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