Bump third_party/pigweed/repo from d5fcc90 to ef5f6bf

Bumps [third_party/pigweed/repo](https://github.com/google/pigweed) from `d5fcc90` to `ef5f6bf`.
- [Commits](google/pigweed@d5fcc90...ef5f6bf)

---
updated-dependencies:
- dependency-name: third_party/pigweed/repo
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>