vm-virtio: pci: Add virtio_device() accessor

Add an accessor to return the underlying VirtioDevice. This is useful
for managing the removal of the device from internal datastructures when
handling virtio-pci device unplug.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vm-virtio/src/transport/pci_device.rs

@@ -564,6 +564,10 @@ impl VirtioPciDevice {
             self.write_bar(0, bar_offset as u64, data)
         }
     }
+
+    pub fn virtio_device(&self) -> Arc<Mutex<dyn VirtioDevice>> {
+        self.device.clone()
+    }
 }
 
 impl VirtioTransport for VirtioPciDevice {