Remove const from `const int loops`.

This drives me nuts, and prevents `while (loops --> 0)`.

BUG=skia:

Review URL: https://codereview.chromium.org/1379923005
diff --git a/bench/MutexBench.cpp b/bench/MutexBench.cpp
index ba92a43..d1d014d 100644
--- a/bench/MutexBench.cpp
+++ b/bench/MutexBench.cpp
@@ -23,7 +23,7 @@
         return fBenchName.c_str();
     }
 
-    void onDraw(const int loops, SkCanvas*) override {
+    void onDraw(int loops, SkCanvas*) override {
         for (int i = 0; i < loops; i++) {
             fMu.acquire();
             fMu.release();
@@ -47,7 +47,7 @@
         return "SkSharedMutexSharedUncontendedBenchmark";
     }
 
-    void onDraw(const int loops, SkCanvas*) override {
+    void onDraw(int loops, SkCanvas*) override {
         for (int i = 0; i < loops; i++) {
             fMu.acquireShared();
             fMu.releaseShared();