sbp-target: fix error path in sbp_make_tpg()

If the TPG memory is allocated successfully, but we fail further along
in the function, a dangling pointer to freed memory is left in the TPort
structure. This is mostly harmless, but does prevent re-trying the
operation without first removing the TPort altogether.
Reported-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Chris Boot <bootc@bootc.net>
Cc: Andy Grover <agrover@redhat.com>
Cc: Nicholas A. Bellinger <nab@linux-iscsi.org>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/sbp/sbp_target.c

@@ -2208,20 +2208,23 @@ static struct se_portal_group *sbp_make_tpg(
 	tport->mgt_agt = sbp_management_agent_register(tport);
 	if (IS_ERR(tport->mgt_agt)) {
 		ret = PTR_ERR(tport->mgt_agt);
-		kfree(tpg);
-		return ERR_PTR(ret);
+		goto out_free_tpg;
 	}
 
 	ret = core_tpg_register(&sbp_fabric_configfs->tf_ops, wwn,
 			&tpg->se_tpg, (void *)tpg,
 			TRANSPORT_TPG_TYPE_NORMAL);
-	if (ret < 0) {
+	if (ret < 0)
+		goto out_unreg_mgt_agt;
+
+	return &tpg->se_tpg;
+
+out_unreg_mgt_agt:
 	sbp_management_agent_unregister(tport->mgt_agt);
+out_free_tpg:
+	tport->tpg = NULL;
 	kfree(tpg);
 	return ERR_PTR(ret);
-	}
-
-	return &tpg->se_tpg;
 }
 
 static void sbp_drop_tpg(struct se_portal_group *se_tpg)