IB/mlx4: Fix bug unwinding on error in mlx4_ib_init_sriov()

We have to decrement "i" before calling mlx4_ib_free_demux_ctx() or we
free something that wasn't allocated.  That's fine for free_pv_object()
but it would lead to a NULL dereference calling mlx4_ib_free_demux_ctx().
The null dereference is because ->tun is NULL when we check:

	if (!ctx->tun[i])

Also we didn't free ->sriov.demux[0] so it was a small leak.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/mlx4/mad.c

@@ -1999,16 +1999,17 @@ int mlx4_ib_init_sriov(struct mlx4_ib_dev *dev)
 			goto demux_err;
 		err = mlx4_ib_alloc_demux_ctx(dev, &dev->sriov.demux[i], i + 1);
 		if (err)
-			goto demux_err;
+			goto free_pv;
 	}
 	mlx4_ib_master_tunnels(dev, 1);
 	return 0;
 
+free_pv:
+	free_pv_object(dev, mlx4_master_func_num(dev->dev), i + 1);
 demux_err:
-	while (i > 0) {
+	while (--i >= 0) {
 		free_pv_object(dev, mlx4_master_func_num(dev->dev), i + 1);
 		mlx4_ib_free_demux_ctx(&dev->sriov.demux[i]);
-		--i;
 	}
 	mlx4_ib_device_unregister_sysfs(dev);