Fix a misnamed variable to fix the build.

Change-Id: Ia69d48ace0a6c10c5e6ea06714e52b8c937e213f
diff --git a/tools/releasetools/build_image.py b/tools/releasetools/build_image.py
index 964f277..2d75749 100755
--- a/tools/releasetools/build_image.py
+++ b/tools/releasetools/build_image.py
@@ -256,7 +256,7 @@
       return False
 
   if run_fsck and prop_dict.get("skip_fsck") != "true":
-    success, unsparse_image_path = UnsparseImage(out_file)
+    success, unsparse_image = UnsparseImage(out_file)
     if not success:
       return False