staging/lustre/lnet: fix potential null pointer dereference

Pointer 'ni' checked for NULL at line 1569 may be passed to
function and may be dereferenced there by passing argument 1 to
function 'lnet_ni_notify_locked' at line 1621.
found by Klocwork Insight tool

Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
CC: Dmitry Eremin <dmitry.eremin@intel.com>
CC: Liang Zhen <liang.zhen@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>