virtio: unbreak virtio-pci with IOMMU after caching ring translations

Commit c611c764 ("virtio: add MemoryListener to cache ring
translations") registers a memory listener to dma_as. This may not
work when IOMMU is enabled: dma_as(bus_master_as) were initialized in
pcibus_machine_done() after virtio_realize(). This will cause a
segfault. Fixing this by using pci_device_iommu_address_space()
instead to make sure address space were initialized at this time.

With this fix, IOMMU device were required to be initialized before any
virtio-pci devices.

Fixes: c611c764 ("virtio: add MemoryListener to cache ring translations")
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NJason Wang <jasowang@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio-pci.c

@@ -1153,7 +1153,7 @@ static AddressSpace *virtio_pci_get_dma_as(DeviceState *d)
     VirtIOPCIProxy *proxy = VIRTIO_PCI(d);
     PCIDevice *dev = &proxy->pci_dev;
 
-    return pci_get_address_space(dev);
+    return pci_device_iommu_address_space(dev);
 }
 
 static int virtio_pci_add_mem_cap(VirtIOPCIProxy *proxy,