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/MatrixConvolutionBench.cpp b/bench/MatrixConvolutionBench.cpp
index 6593ab0..6302f12 100644
--- a/bench/MatrixConvolutionBench.cpp
+++ b/bench/MatrixConvolutionBench.cpp
@@ -35,7 +35,7 @@
         return fName.c_str();
     }
 
-    virtual void onDraw(const int loops, SkCanvas* canvas) {
+    virtual void onDraw(int loops, SkCanvas* canvas) {
         SkPaint paint;
         this->setupPaint(&paint);
         paint.setAntiAlias(true);