[roll third_party/pigweed] pw_sys_io: Doxygenify TryReadByte()

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/153190

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 7d1c4f21fd054bf..3985099a5466144
Roller-URL: https://ci.chromium.org/b/8777190727108019089
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ie2dbee572ad88c42850efe70d7396e2c3f9fe68a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/153235
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 7d1c4f2..3985099 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 7d1c4f21fd054bfc325c9e922a430fc5aba4b7fd
+Subproject commit 3985099a54661443c749a0a45e9839d2302fc49f