s390/topology: fix typo in early topology code

Use MACHINE_FLAG_TOPOLOGY instead of MACHINE_HAS_TOPOLOGY when
clearing the bit that indicates if the machine provides topology
information (and if it should be used). Currently works anyway.

Fixes: 68cc795d ("s390/topology: make "topology=off" parameter work")
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>