sandbox: usb: Convert emulators to livetree

Update the sandbox flash and hub USB emulators to support a live device
tree.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/usb/emul/sandbox_hub.c b/drivers/usb/emul/sandbox_hub.c
index f0939b1..9ffda9c 100644
--- a/drivers/usb/emul/sandbox_hub.c
+++ b/drivers/usb/emul/sandbox_hub.c
@@ -277,8 +277,7 @@
 {
 	struct sandbox_hub_platdata *plat = dev_get_parent_platdata(dev);
 
-	plat->port = fdtdec_get_int(gd->fdt_blob, dev_of_offset(dev), "reg",
-				    -1);
+	plat->port = dev_read_u32_default(dev, "reg", -1);
 
 	return 0;
 }