pw_log_string: Bazel build fix

The pw_log_string should only depend on the handler facade to avoid
circular dependencies.

Bug: b/255431090
Change-Id: I98ef671149bcb9cb1d260eba0a2b43571b3bf143
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/137734
Pigweed-Auto-Submit: Ted Pudlik <tpudlik@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>

pw_log_string/BUILD.bazel

@@ -33,7 +33,7 @@ pw_cc_library(
         "public_overrides",
     ],
     deps = [
-        ":handler",
+        ":handler_facade",
         "//pw_preprocessor",
     ],
 )