s390/mm: Fix ERROR: "__node_distance" undefined!

Fixes:
ERROR: "__node_distance" [drivers/nvme/host/nvme-core.ko] undefined!
make[1]: *** [scripts/Makefile.modpost:92: __modpost] Error 1
make: *** [Makefile:1275: modules] Error 2
+ exit 1

Signed-off-by: Justin M. Forbes <jforbes@fedoraproject.org>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>