virtio-devices: Implement VirtioDevice::access_platform()

This forwards through to the VirtioCommon implementation and can be used
to simplify the virtio PCI access code.

Signed-off-by: Rob Bradford <rbradford@meta.com>

virtio-devices/src/vsock/device.rs

@@ -501,6 +501,10 @@ where
     fn set_access_platform(&mut self, access_platform: Arc<dyn AccessPlatform>) {
         self.common.set_access_platform(access_platform);
     }
+
+    fn access_platform(&self) -> Option<Arc<dyn AccessPlatform>> {
+        self.common.access_platform()
+    }
 }
 
 impl<B> Pausable for Vsock<B>