staging: lustre: Fix possible NULL pointer dereference in lprocfs_status.c

The imp->imp_connection really could be NULL, we better check for it
before dereferencing it in taht call to libcfs_nid2str_r.

Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-6507
Reviewed-on: http://review.whamcloud.com/14808


Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>