[llvm-mca] Fix use-of-uninitialized-value error reported by the MemorySanitizer.

This should make the buildbots green again.

llvm-svn: 327223
diff --git a/llvm/tools/llvm-mca/BackendStatistics.h b/llvm/tools/llvm-mca/BackendStatistics.h
index f5363bd..04fa912 100644
--- a/llvm/tools/llvm-mca/BackendStatistics.h
+++ b/llvm/tools/llvm-mca/BackendStatistics.h
@@ -108,7 +108,7 @@
 
 public:
   BackendStatistics(const Backend &backend)
-      : B(backend), NumDispatched(0), NumIssued(0), NumRetired(0) {}
+      : B(backend), NumDispatched(0), NumIssued(0), NumRetired(0), NumCycles(0) {}
 
   void onInstructionDispatched(unsigned Index) override { NumDispatched++; }
   void