LU-3772 ptlrpc: fix nrs cleanup

LU-3772 ptlrpc: fix nrs cleanup

When service start failed due to short of memory, the cleanup code
could operate on uninitialized structure and cause crash at the end.

This patch fix the nrs_svcpt_cleanup_locked() to perform cleanup only
on the nrs which has been properly initialized.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: Ieafa5b144133490b662f5a80a7b99311a9970de3
Reviewed-on: http://review.whamcloud.com/7410
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>