s390/dcssblk: Add missing MODULE_DESCRIPTION() macro

With ARCH=s390, make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/s390/block/dcssblk.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-drivers-s390-block-dcssblk-v1-1-d9d19703abcb@quicinc.com


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