[roll third_party/pigweed] pw_rpc: Prefix Nanopb struct names with "::"

This prevents prevents Nanopb names from incorrectly resolving to names
in namespaces.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/68096

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 1b69a4ec6ac6145..9a5210dc2b50081
Roller-URL: https://ci.chromium.org/b/8830473639229515937
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8830473639229515937
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I2af8553a4130e2d2f06e75a3aaa5ad6299accec4
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/68903
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 1b69a4e..9a5210d 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 1b69a4ec6ac61457e57e9bcb8591448b573f2ff4
+Subproject commit 9a5210dc2b5008149e774fb1dd756d78e2630319