net: vxge: fix use-after-free in vxge_device_unregister

Smatch says:
drivers/net/ethernet/neterion/vxge/vxge-main.c:3518 vxge_device_unregister() error: Using vdev after free_{netdev,candev}(dev);
drivers/net/ethernet/neterion/vxge/vxge-main.c:3518 vxge_device_unregister() error: Using vdev after free_{netdev,candev}(dev);
drivers/net/ethernet/neterion/vxge/vxge-main.c:3520 vxge_device_unregister() error: Using vdev after free_{netdev,candev}(dev);
drivers/net/ethernet/neterion/vxge/vxge-main.c:3520 vxge_device_unregister() error: Using vdev after free_{netdev,candev}(dev);

Since vdev pointer is netdev private data accessing it after free_netdev()
call can cause use-after-free bug. Fix it by moving free_netdev() call at
the end of the function

Fixes: 6cca2003 ("vxge: cleanup probe error paths")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/neterion/vxge/vxge-main.c

@@ -3512,13 +3512,13 @@ static void vxge_device_unregister(struct __vxge_hw_device *hldev)
 
 	kfree(vdev->vpaths);
 
-	/* we are safe to free it now */
-	free_netdev(dev);
-
 	vxge_debug_init(vdev->level_trace, "%s: ethernet device unregistered",
 			buf);
 	vxge_debug_entryexit(vdev->level_trace,	"%s: %s:%d  Exiting...", buf,
 			     __func__, __LINE__);
+
+	/* we are safe to free it now */
+	free_netdev(dev);
 }
 
 /*