Add ClobberMemory to count_min update benchmarks

benchmarks/benchmark_count_min_sketch.cpp

diff --git a/benchmarks/benchmark_count_min_sketch.cpp b/benchmarks/benchmark_count_min_sketch.cpp
index 9bbff0f..34fbecb 100644
--- a/benchmarks/benchmark_count_min_sketch.cpp
+++ b/benchmarks/benchmark_count_min_sketch.cpp
@@ -73,6 +73,7 @@
         for (const auto key : keys)
             sketch.update(&key, sizeof(key), 1);
 
+        benchmark::ClobberMemory();
         benchmark::DoNotOptimize(sketch.get_total_weight());
     }
 
@@ -94,6 +95,7 @@
         for (const auto & key : keys)
             sketch.update(key.data(), key.size(), 1);
 
+        benchmark::ClobberMemory();
         benchmark::DoNotOptimize(sketch.get_total_weight());
     }