[roll third_party/pigweed] pw_random: Fix implicit conversions in RandomGenerator

Fix implicit conversion from int to uint8_t in
RandomGenerator::CountLeadingZeros. This conversion is safe because
the __builtin_clz functions always return a positive value <= 64.

This fixed compilation on Fuchsia.

Test: pw watch
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/126510

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 858b99a34b69f57..723880e79fdda9f
Roller-URL: https://ci.chromium.org/b/8792059001065474449
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I83835334e85b0454bbaad4ac143940b98d256ba0
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/126511
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 858b99a..723880e 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 858b99a34b69f577a83ecf8d91fcce2555d1c08f
+Subproject commit 723880e79fdda9f537a911f88983229d44006e0c