[llvm-exegesis][NFC] Use an enum instead of a string for benchmark mode.

Summary: YAML encoding is backwards-compatible.

Reviewers: gchatelet

Subscribers: tschuett, llvm-commits

Differential Revision: https://reviews.llvm.org/D47705

llvm-svn: 333886
diff --git a/llvm/unittests/tools/llvm-exegesis/BenchmarkResultTest.cpp b/llvm/unittests/tools/llvm-exegesis/BenchmarkResultTest.cpp
index 33b139c..d3e3a5f 100644
--- a/llvm/unittests/tools/llvm-exegesis/BenchmarkResultTest.cpp
+++ b/llvm/unittests/tools/llvm-exegesis/BenchmarkResultTest.cpp
@@ -28,7 +28,7 @@
   InstructionBenchmark ToDisk;
 
   ToDisk.Key.OpcodeName = "name";
-  ToDisk.Key.Mode = "mode";
+  ToDisk.Key.Mode = InstructionBenchmarkKey::Latency;
   ToDisk.Key.Config = "config";
   ToDisk.CpuName = "cpu_name";
   ToDisk.LLVMTriple = "llvm_triple";