[S390] sclp: fix possible deadlock on cpu rescan.
smp_rescan_cpus() calls get_online_cpus() from a multithreaded workqueue context. This may deadlock. This is the same bug as in arch/s390/kernel/topology.c. This patch can be reverted as soon as Oleg's patch gets merged. Signed-off-by: Heiko Carstens <firstname.lastname@example.org> Signed-off-by: Martin Schwidefsky <email@example.com>