s390/topology: always use s390 specific sched_domain_topology_level

The s390 specific sched_domain_topology_level should always be used,
not only if the machine provides topology information. Luckily this
odd behaviour, that was by accident introduced with git commit
d05d15da ("s390/topology: delay initialization of topology cpu
masks") has currently no side effect.

Fixes: d05d15da ("s390/topology: delay initialization of topology cpumasks")
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>