virtio_blk: zone append in header type tweak

virtio blk returns a 64 bit append_sector in an input buffer,
in LE format. This field is not tagged as LE correctly, so
even though the generated code is ok, we get warnings from sparse:

drivers/block/virtio_blk.c:332:33: sparse: sparse: cast to restricted __le64

Make sparse happy by using the correct type.

Message-Id: <20221220125154.564265-1-mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>