dlm: constify kset_uevent_ops structure

Declare kset_uevent_ops structure as const as it is only passed as an
argument to the function kset_create_and_add. This argument is of type
const, so declare the structure as const.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: David Teigland <teigland@redhat.com>