[roll third_party/pigweed] pw_ring_buffer: Correct documentation

A few minor documentation fixes:

1. The buffer is now provided by an explicit call to SetBuffer().
2. Use the `buffer` member of the Entry/iterator.
3. Cast to unsigned for correct string formatting.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/126217

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 4f10c431a51eb19..651e2bc3cae77d2
Roller-URL: https://ci.chromium.org/b/8792319121841605297
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ie739e74d79103aae8c09e9d49fe4305e58147d6a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/126345
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 4f10c43..651e2bc 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 4f10c431a51eb1929944653645bca992c17b140b
+Subproject commit 651e2bc3cae77d25bf039b9448192bf31ce4c34b