Kernel: Specify default memory order for some non-synchronizing Atomics

Author: https://github.com/tomuta
Commit: 901ef3f1c8
Pull-request: https://github.com/SerenityOS/serenity/pull/4783

Kernel/FileSystem/Plan9FileSystem.cpp

@@ -679,7 +679,7 @@ void Plan9FS::thread_main()
             dbg() << "Plan9FS: Thread terminating, error reading";
             return;
         }
-    } while (!m_thread_shutdown.load(AK::MemoryOrder::memory_order_relaxed));
+    } while (!m_thread_shutdown);
     dbg() << "Plan9FS: Thread terminating";
 }