staging: lustre: fix framework.c issues found by Klocwork Insight tool

staging: lustre: fix framework.c issues found by Klocwork Insight tool

The functions sfw_test_buffers() and sfw_unload_test() from LNet
selftest both assume sfw_test_instance_t being passed in is never
null. This is corrected here.

Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4629
Reviewed-on: http://review.whamcloud.com/9386
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Isaac Huang <he.huang@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>