LU-6142 lod: remove unnecessary variables

LU-6142 lod: remove unnecessary variables

Both lprocfs_register() and dt_tunables_init() treat a NULL pointer as
being equivalent to an empty array.

So discard the empty arrays and use the NULL pointer.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I620fbf1c771ee80d2ddff0f38a87c2f08bae0e4d
Reviewed-on: https://review.whamcloud.com/41766
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>