virtio-devices: vsock: Adapt used handling to match other devices

Follow the same pattern as other virtio devices using a bool to check if
it needs notification and propagating its own Error enum.

Sadly this does still use `anyhow!()` but this does match with the
behaviour of the other devices in their implementations.

As a side effect we can now remove two errors from the top-level Error
enum in virtio-devices as these were only used by this module and those
errors had mangled descriptions.

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

virtio-devices/src/lib.rs

@@ -117,10 +117,6 @@ pub enum Error {
     SetShmRegionsNotSupported,
     #[error("Failed to process net queue")]
     NetQueuePair(#[source] ::net_util::NetQueuePairError),
-    #[error("Failed to ")]
-    QueueAddUsed(#[source] virtio_queue::Error),
-    #[error("Failed to ")]
-    QueueIterator(#[source] virtio_queue::Error),
 }
 
 #[derive(Clone, Copy, Debug, Default, Deserialize, Serialize, PartialEq, Eq)]