virtio: sandbox: Bind RNG rather than block device

The virtio-rng driver is extremely simple, making it suitable for
testing more of the virtio uclass logic. Have the sandbox driver bind
the virtio-rng driver rather than the virtio-blk driver so it can be
used in tests.

Signed-off-by: Andrew Scull <ascull@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/virtio_device.c b/test/dm/virtio_device.c
index 46f4798..f5f2349 100644
--- a/test/dm/virtio_device.c
+++ b/test/dm/virtio_device.c
@@ -25,10 +25,10 @@
 	ut_assertok(uclass_first_device(UCLASS_VIRTIO, &bus));
 	ut_assertnonnull(bus);
 
-	/* check the child virtio-blk device is bound */
+	/* check the child virtio-rng device is bound */
 	ut_assertok(device_find_first_child(bus, &dev));
 	ut_assertnonnull(dev);
-	ut_assertok(strcmp(dev->name, "virtio-blk#0"));
+	ut_asserteq_str("virtio-rng#0", dev->name);
 
 	/* check driver status */
 	ut_assertok(virtio_get_status(dev, &status));