s390/mm: Add missing MODULE_DESCRIPTION() macro

With ARCH=s390, make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in arch/s390/mm/cmm.o

Add the missing invocation of the MODULE_DESCRIPTION() macro.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Link: https://lore.kernel.org/r/20240615-md-s390-arch-s390-mm-v1-1-a360eed8c7c3@quicinc.com


Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>