[roll pigweed] pw_log_null: implement PW_HANDLE_LOG

PW_HANDLE_LOG is used by pw_assert_log, but isn't implemented by
log_null today which causes a build breakage.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/105181

https://pigweed.googlesource.com/pigweed/pigweed
pigweed Rolled-Commits: 4c3481a61da6d73..979a6da6de04de4
Roller-URL: https://ci.chromium.org/b/8806388233649105361
Cq-Cl-Tag: roller-builder:pigweed-zephyr-roller
Cq-Cl-Tag: roller-bid:8806388233649105361
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I09f53d51d70115ccf4db9de5c41f4b1a3f10c674
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/zephyr-integration/+/105420
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/pigweed b/pigweed
index 4c3481a..979a6da 160000
--- a/pigweed
+++ b/pigweed
@@ -1 +1 @@
-Subproject commit 4c3481a61da6d73c44952cd3975a1ecf682e7988
+Subproject commit 979a6da6de04de4c6d112134bbda75f54eac418b