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/include/expo.h b/include/expo.h
index 42e934e..84dc77f 100644
--- a/include/expo.h
+++ b/include/expo.h
@@ -194,14 +194,14 @@
 /**
  * struct scene_obj_bbox - Dimensions of an object
  *
- * @x: x position, in pixels from left side
- * @y: y position, in pixels from top
+ * @x0: x position, in pixels from left side
+ * @y0: y position, in pixels from top
  * @w: width, in pixels
  * @h: height, in pixels
  */
 struct scene_obj_bbox {
-	int x;
-	int y;
+	int x0;
+	int y0;
 	int w;
 	int h;
 };