vdpa: fix use-after-free on vp_vdpa_remove

When vp_vdpa driver is unbind, vp_vdpa is freed in vdpa_unregister_device
and then vp_vdpa->mdev.pci_dev is dereferenced in vp_modern_remove,
triggering use-after-free.

Call Trace of unbinding driver free vp_vdpa :
do_syscall_64
vfs_write
kernfs_fop_write_iter
device_release_driver_internal
pci_device_remove
vp_vdpa_remove
vdpa_unregister_device
kobject_release
device_release
kfree

Call Trace of dereference vp_vdpa->mdev.pci_dev:
vp_modern_remove
pci_release_selected_regions
pci_release_region
pci_resource_len
pci_resource_end
(dev)->resource[(bar)].end

Signed-off-by: Zhang Min <[e-mail]>
Signed-off-by: Yi Wang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Michael S. Tsirkin <[e-mail]>
Fixes: 64b9f64f80a6 ("vdpa: introduce virtio pci driver")
Reviewed-by: Stefano Garzarella <[e-mail]>

drivers/vdpa/virtio_pci/vp_vdpa.c

···
 {
 	struct vp_vdpa *vp_vdpa = pci_get_drvdata(pdev);
 
-	vdpa_unregister_device(&vp_vdpa->vdpa);
 	vp_modern_remove(&vp_vdpa->mdev);
+	vdpa_unregister_device(&vp_vdpa->vdpa);
 }
 
 static struct pci_driver vp_vdpa_driver = {