pw_thread: Fix pw_thread_zephyr compilability

It was broken by https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/205760.

Change-Id: Id57cb028369ab411674c8ae9ca8c5d83f3fa52e5
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/206970
Commit-Queue: Alexey Eremin <aeremin@google.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Reviewed-by: Rob Mohr <mohrr@google.com>
diff --git a/pw_thread_zephyr/public/pw_thread_zephyr/context.h b/pw_thread_zephyr/public/pw_thread_zephyr/context.h
index af579cf..bbdfede 100644
--- a/pw_thread_zephyr/public/pw_thread_zephyr/context.h
+++ b/pw_thread_zephyr/public/pw_thread_zephyr/context.h
@@ -80,7 +80,7 @@
 
   k_tid_t task_handle_ = nullptr;
   k_thread thread_info_;
-  DeprecatedOrNewThreadFn fn;
+  DeprecatedOrNewThreadFn fn_;
   bool detached_ = false;
   bool thread_done_ = false;
 };