vfio/pci: Remove vfio_detach_device from vfio_realize error path
In vfio_realize, on the error path, we currently call
vfio_detach_device() after a successful vfio_attach_device.
While this looks natural, vfio_instance_finalize also induces
a vfio_detach_device(), and it seems to be the right place
instead as other resources are released there which happen
to be a prerequisite to a successful UNSET_CONTAINER.
So let's rely on the finalize vfio_detach_device call to free
all the relevant resources.