[roll third_party/pigweed] pw_multibuf: Fix soong support

Expose the pw_multibuf module as a cc_defaults to avoid injecting
unexpected backends silently.

Original-Bug: 325320103
Tested: builds in android project
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/192894

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 8b408829fcd8b9d..e982c93aba2cc25
Roller-URL: https://ci.chromium.org/b/8755915111824399441
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Iab4a25ae763beaceec79209dcf7b10f4024ad73c
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/192873
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 8b40882..e982c93 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 8b408829fcd8b9d74d49bf0f2d23554a7461e3b6
+Subproject commit e982c93aba2cc259e65cc3e518ecf3230e5d2d9f