tools/virtio: switch to __ptr_ring_empty

We don't rely on lockless guarantees, but it
seems cleaner than inverting __ptr_ring_peek.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/virtio/ringtest/ptr_ring.c

@@ -187,7 +187,7 @@ bool enable_kick()
 
 bool avail_empty()
 {
-	return !__ptr_ring_peek(&array);
+	return __ptr_ring_empty(&array);
 }
 
 bool use_buf(unsigned *lenp, void **bufp)