[roll third_party/pigweed] pw_channel: Return status from PollReadyToWrite

This status allows the caller to know if the channel has closed before
preparing a write buffer.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/200995

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 990b5f8ea0be1cc..f37576a00cd3542
Roller-URL: https://ci.chromium.org/b/8751839127292730657
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I3dff1862dd84969d428a2f0215defd773fa48bb6
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/201254
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 990b5f8..f37576a 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 990b5f8ea0be1cc97f743253c5a7da516a1e0170
+Subproject commit f37576a00cd35423d92f67746bada9778037f211