CVE-2022-48899 drm/virtio: Fix GEM handle creation UAF

In the Linux kernel, the following vulnerability has been resolved:

drm/virtio: Fix GEM handle creation UAF

Userspace can guess the handle value and try to race GEM object creation
with handle close, resulting in a use-after-free if we dereference the
object after dropping the handle’s reference. For that reason, dropping
the handle’s reference must be done after we are done dereferencing
the object.