staging/lustre: const correct set_lock_data()

Change the __u64 *cookie parameter of md_ops->set_lock_data() to
const struct lustre_handle *lockh.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Reviewed-on: http://review.whamcloud.com/17072
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-7403


Reviewed-by: Frank Zago <fzago@cray.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>