staging/lustre/mdc: fix issue found by Klocwork Insight tool

Pointer 'mod' checked for NULL at line 160 may be dereferenced at line 208.
Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-on: http://review.whamcloud.com/9387
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4629Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/mdc/mdc_reint.c

@@ -199,7 +199,8 @@ int mdc_setattr(struct obd_export *exp, struct md_op_data *op_data,
 	*request = req;
 	if (rc && req->rq_commit_cb) {
 		/* Put an extra reference on \var mod on error case. */
-		obd_mod_put(*mod);
+		if (mod != NULL && *mod != NULL)
+			obd_mod_put(*mod);
 		req->rq_commit_cb(req);
 	}
 	return rc;