Bluetooth: Simplify started check

Test: Bluetooth starts/stops
Change-Id: Ib1777ac31d4a13d4221045fa3fa7d817a795f6f9
diff --git a/bluetooth/1.0/default/async_fd_watcher.cc b/bluetooth/1.0/default/async_fd_watcher.cc
index a88aa27..287d007 100644
--- a/bluetooth/1.0/default/async_fd_watcher.cc
+++ b/bluetooth/1.0/default/async_fd_watcher.cc
@@ -41,12 +41,7 @@
   }
 
   // Start the thread if not started yet
-  int started = tryStartThread();
-  if (started != 0) {
-    return started;
-  }
-
-  return 0;
+  return tryStartThread();
 }
 
 int AsyncFdWatcher::ConfigureTimeout(