LU-11838 lustre: discard LTIME_S macro

LU-11838 lustre: discard LTIME_S macro

Rather than using a macro, just access the required
field directly.

Linux-commit: 5b7cc4e4ce3cc15f67462ae75c55eecc7edc3a40

This patch is back-ported from the following one:
Lustre-commit: 65a8ff5fbe8ca014bd01150ab102d8aa43f78cff
Lustre-change: https://review.whamcloud.com/33984

Change-Id: I325cac7458265d1cf6ad9f195a513f2612865906
Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-on: https://review.whamcloud.com/35169
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>