[third_party/pigweed] Roll 2 commits

a19e285f417b081 pw_varint: Add function to read from stream
8fe2829be9ee25a pw_software_udpate: Write user_manifest

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: ecf3d8074d5cb53..a19e285f417b081
Roller-URL: https://ci.chromium.org/b/8827736509261650129
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8827736509261650129
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ie7303030064b52d7f7f1ba4d8d78b9a3e58d8cba
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/74820
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 ecf3d80..a19e285 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit ecf3d8074d5cb53a372db70848c7136070d84325
+Subproject commit a19e285f417b08146234a54878e826ef61b9defa