kleaf: checkpatch_presubmit: Find repo root from workspace directory am: 23f1cd3485

Original change: https://android-review.googlesource.com/c/kernel/build/+/4014466

Change-Id: I49e468651b55975ecf8bf6374b5f35186a236fa7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>