LU-3649 lfsck: release object reference when reset lfsck

LU-3649 lfsck: release object reference when reset lfsck

When reset lfsck, related lfsck tracing file will be re-created,
but we forgot to release the object reference of the old tracing
file, then trigger LASSERT() when related device to be released.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I657e539183675e00fe43bbbdfde987c3e48dd13b
Reviewed-on: http://review.whamcloud.com/7432
Tested-by: Hudson
Reviewed-by: Patrick Farrell <paf@cray.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>