staging: lustre: 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>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3772
Reviewed-on: http://review.whamcloud.com/7410


Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>