[roll third_party/pigweed] pw_rpc: Don't hold the RPC lock when calling AcquireBuffer

This updates RPC calls to release their buffer before calling
Channel::AcquireBuffer to prevent potential deadlocks if the
ChannelOutput has its own locking.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/77960

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 3ce31ccbd3cad5b..e4a0a67c425eec9
Roller-URL: https://ci.chromium.org/b/8825369398586737025
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8825369398586737025
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ide4a4ee712faa49a7080a4613ce9e827df18128b
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/77981
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 3ce31cc..e4a0a67 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 3ce31ccbd3cad5b72fdf103c7dcd5969487b14ae
+Subproject commit e4a0a67c425eec93c924d83edb446572f9ab4277