[S390] reset default for CONFIG_CHSC_SCH

6f9a3c33 "[S390] cleanup s390 Kconfig" accidentally changed
the default for CONFIG_CHSC_SCH. Reset it to m.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>