[roll third_party/pigweed] docs: Fix broken links

Tested by following the links in locally built documentation.

Original-Fixed: 558
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/72461

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 7e13e366b9c470b..89147b391efa687
Roller-URL: https://ci.chromium.org/b/8825739269799826865
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8825739269799826865
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I8aec9cd9d0141f0829d3a048327ee682506072b0
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/77401
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 7e13e36..89147b3 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 7e13e366b9c470bc8e0e939d28369ffe065add0e
+Subproject commit 89147b391efa6878cbca1976f12c3f9e3d854214