LU-6177 lfsck: calculate the phase2 time correctly

LU-6177 lfsck: calculate the phase2 time correctly

When the second-stage scanning finished, the assistant thread will
calculate how long the phase2 scanning has consumed by calling the
la_double_scan_result(). It should use com->lc_time_last_checkpoint,
(unfortunately it used lfsck->li_time_last_checkpoint by wrong) for
that.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I96cfdf615038f52aea0df33930226155ca61ce9b
Reviewed-on: http://review.whamcloud.com/14014
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>