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/MergeBench.cpp b/bench/MergeBench.cpp
index 404f646..925b6b2 100644
--- a/bench/MergeBench.cpp
+++ b/bench/MergeBench.cpp
@@ -33,7 +33,7 @@
         }
     }
 
-    void onDraw(const int loops, SkCanvas* canvas) override {
+    void onDraw(int loops, SkCanvas* canvas) override {
         SkRect r = fIsSmall ? SkRect::MakeWH(FILTER_WIDTH_SMALL, FILTER_HEIGHT_SMALL) :
                               SkRect::MakeWH(FILTER_WIDTH_LARGE, FILTER_HEIGHT_LARGE);
         SkPaint paint;