payload_utils: Fix import paths after proto reorg.

- crrev.com/c/2055732 added "proto" to import path.

BUG=chromium:1051187
TEST=python3 -m unittest discover -p *test.py

Change-Id: I6c8dda734a11ceae006def1f6f04aa45c15d332b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/config/+/2057383
Commit-Queue: Andrew Lamb <andrewlamb@chromium.org>
Commit-Queue: David Burger <dburger@chromium.org>
Tested-by: Andrew Lamb <andrewlamb@chromium.org>
Auto-Submit: Andrew Lamb <andrewlamb@chromium.org>
Reviewed-by: David Burger <dburger@chromium.org>
diff --git a/payload_utils/checker/io_utils.py b/payload_utils/checker/io_utils.py
index a327efe..8044429 100644
--- a/payload_utils/checker/io_utils.py
+++ b/payload_utils/checker/io_utils.py
@@ -5,7 +5,7 @@
 
 import os
 
-from bindings.src.config.api import config_bundle_pb2
+from bindings.src.config.proto.api import config_bundle_pb2
 
 
 def read_repo_config(repo_path: str) -> config_bundle_pb2.ConfigBundle: