expo: Rename x and y in struct scene_obj_bbox

These coordinates are the top left values, so rename them to x0 and y0
in preparation for changing the width and height to x1 and y1

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/scene_menu.c b/boot/scene_menu.c
index 20a6a6b..c47c203 100644
--- a/boot/scene_menu.c
+++ b/boot/scene_menu.c
@@ -102,7 +102,7 @@
 		label = scene_obj_find(scn, item->label_id, SCENEOBJT_NONE);
 
 		ret = scene_obj_set_pos(scn, menu->pointer_id,
-					menu->obj.bbox.x + 200, label->bbox.y);
+					menu->obj.bbox.x0 + 200, label->bbox.y0);
 		if (ret < 0)
 			return log_msg_ret("ptr", ret);
 	}
@@ -205,12 +205,12 @@
 	int x, y;
 	int ret;
 
-	x = menu->obj.bbox.x;
-	y = menu->obj.bbox.y;
+	x = menu->obj.bbox.x0;
+	y = menu->obj.bbox.y0;
 	if (menu->title_id) {
 		int width;
 
-		ret = scene_obj_set_pos(scn, menu->title_id, menu->obj.bbox.x, y);
+		ret = scene_obj_set_pos(scn, menu->title_id, menu->obj.bbox.x0, y);
 		if (ret < 0)
 			return log_msg_ret("tit", ret);