Work around new clang compiler warning.

Bug: 38322617
Test: build with WITH_TIDY=1
Change-Id: I71c63571e42a68f1d70ee97cbf5cb8468cba1bf0
diff --git a/tests/benchmarks/connect_benchmark.cpp b/tests/benchmarks/connect_benchmark.cpp
index 384feb1..132844c 100644
--- a/tests/benchmarks/connect_benchmark.cpp
+++ b/tests/benchmarks/connect_benchmark.cpp
@@ -171,7 +171,7 @@
     if (iterations > 0) {
         latencies.resize(iterations);
         sort(latencies.begin(), latencies.end());
-        state.SetLabel(StringPrintf("%lld", (long long) latencies[iterations * 9 / 10]));
+        state.SetLabel(StringPrintf("%lld", (long long) latencies[iterations * 9 / 10]).c_str());
     }
 }
 
@@ -228,7 +228,7 @@
     if (iterations > 0) {
         latencies.resize(iterations);
         sort(latencies.begin(), latencies.end());
-        state.SetLabel(StringPrintf("%lld", (long long) latencies[iterations * 9 / 10]));
+        state.SetLabel(StringPrintf("%lld", (long long) latencies[iterations * 9 / 10]).c_str());
     }
 }