Fix return-stack-address warning am: 1a39569491 am: a8d7eb6729 am: 952c2c7ce7

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/2462897

Change-Id: I6325872219220baa3371b810a4714ac882bb3275
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
diff --git a/keymaster/4.0/vts/performance/Benchmark.cpp b/keymaster/4.0/vts/performance/Benchmark.cpp
index 96ef5bf..e5fdff2 100644
--- a/keymaster/4.0/vts/performance/Benchmark.cpp
+++ b/keymaster/4.0/vts/performance/Benchmark.cpp
@@ -315,7 +315,7 @@
 
     SecurityLevel getSecurityLevel() { return securityLevel_; }
 
-    const string& GenerateMessage(int size) {
+    const string GenerateMessage(int size) {
         for (const string& message : message_cache_) {
             if (message.size() == size) {
                 return message;
@@ -323,7 +323,7 @@
         }
         string message = string(size, 'x');
         message_cache_.push_back(message);
-        return std::move(message);
+        return message;
     }
 
     optional<BlockMode> getBlockMode(string transform) {
@@ -714,4 +714,4 @@
         return 1;
     }
     ::benchmark::RunSpecifiedBenchmarks();
-}
\ No newline at end of file
+}