Rename a status enum member for Mutex::TryLock.

I changed it to kLockFailed, because kUnlocked seemed not to be a
particularly descriptive name.

Change-Id: Ifdb2ecbf0837cc4b6c40036eedd35d609ada747f
diff --git a/aos/common/condition_test.cc b/aos/common/condition_test.cc
index 05990e5..2310273 100644
--- a/aos/common/condition_test.cc
+++ b/aos/common/condition_test.cc
@@ -307,7 +307,7 @@
   Settle();
   shared_->condition.Signal();
   EXPECT_FALSE(child.Hung());
-  EXPECT_EQ(Mutex::State::kUnlocked, shared_->mutex.TryLock());
+  EXPECT_EQ(Mutex::State::kLockFailed, shared_->mutex.TryLock());
 }
 
 // Tests that Signal() stops exactly 1 Wait()er.