staging/lustre: clean up SET_BUT_UNUSED/UNUSED macros

This is SET_BUT_UNUSED/UNUSED macro cleaning up part
of the original Lustre tree commit.

Lustre-change: http://review.whamcloud.com/6139
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3204
Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Signed-off-by: Ned Bass <bass6@llnl.gov>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Peng Tao <bergwolf@gmail.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>