LU-2960 lmv: typo fix for output of "lfs mdts"

Using ltd_idx(in lmv_tgt_descs) directly for the output of
lctl get_params lustre.lmv.*-clilmv-*.target_obd.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: I6a4ff4b82e4d413baf1f36f85764d3c11cd82435
Reviewed-on: http://review.whamcloud.com/5782
Tested-by: Hudson
Reviewed-by: Li Wei <wei.g.li@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>