[roll third_party/pigweed] docs: Fix broken link

Tested by reviewing the generated docs in a browser.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/73520

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: c62a2d2d66bce61..f228b41839edb40
Roller-URL: https://ci.chromium.org/b/8828203365909889649
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8828203365909889649
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I8ba053954d5aa5da3874ecca9e91350abc515a24
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/73540
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index c62a2d2..f228b41 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit c62a2d2d66bce615bbf5814ff004553bd8ef9dd9
+Subproject commit f228b41839edb40b8b3ffda3516c7144fd2626b6