dlm: Fix kernel memory disclosure

Clear the 'unused' field and the uninitialized padding in 'lksb' to
avoid leaking memory to userland in copy_result_to_user().

Signed-off-by: Vlad Tsyrklevich <vlad@tsyrklevich.net>
Signed-off-by: David Teigland <teigland@redhat.com>