manifest: Use forked chromite repository.

This CL is changing the chromite repository that will be checked-out and
used for builds. Apart from that it is also using the head of
release-R81-12871.B for chromite repository instead of using
a particular commit. This repository can be used for carrying patches on
top of ChromeOS chromite repo.

BUG=b/171561057
TEST=repo init and sync

Change-Id: Iefd25eda621aeb699936b69f7287ea7041eab00c
Reviewed-on: https://cos-review.googlesource.com/c/cos/manifest/+/12950
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Tested-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
diff --git a/external_full.xml b/external_full.xml
index f79b7f4..de2fd43 100644
--- a/external_full.xml
+++ b/external_full.xml
@@ -27,9 +27,6 @@
   </notice>
 
   <!-- mirrored cros_sdk dependencies -->
-  <project path="chromite"
-           name="mirrors/cros/chromiumos/chromite"
-           revision="d2be92f28c64dea085e813227717c7422c995b0a" />
   <project path="chromite/infra/proto"
            name="mirrors/cros/chromiumos/infra/proto"
            revision="4bcb4b7260bf9b98f93f5c3be79564c9ab206ce9" />
@@ -94,6 +91,11 @@
            name="third_party/kernel"
            revision="refs/heads/main-R81-12871.B-cos-4.19" />
 
+  <!-- forked cros_sdk dependencies -->
+  <project path="chromite"
+           name="third_party/chromite"
+           revision="refs/heads/release-R81-12871.B" />
+
   <repo-hooks enabled-list="pre-upload"
            in-project="cos/repohooks" />