s390/ctcm: Convert sysfs sprintf to sysfs_emit

Following the advice of the Documentation/filesystems/sysfs.rst.
All sysfs related show()-functions should only use sysfs_emit() or
sysfs_emit_at() when formatting the value to be returned to user space.

Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Thorsten Winkler <twinkler@linux.ibm.com>
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>