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/DisplacementBench.cpp b/bench/DisplacementBench.cpp
index d9ddc8b..f3f9472 100644
--- a/bench/DisplacementBench.cpp
+++ b/bench/DisplacementBench.cpp
@@ -100,7 +100,7 @@
         return this->isSmall() ? "displacement_zero_small" : "displacement_zero_large";
     }
 
-    void onDraw(const int loops, SkCanvas* canvas) override {
+    void onDraw(int loops, SkCanvas* canvas) override {
         SkPaint paint;
         SkAutoTUnref<SkImageFilter> displ(SkImageSource::Create(fCheckerboard));
         // No displacement effect
@@ -127,7 +127,7 @@
         return isSmall() ? "displacement_alpha_small" : "displacement_alpha_large";
     }
 
-    void onDraw(const int loops, SkCanvas* canvas) override {
+    void onDraw(int loops, SkCanvas* canvas) override {
         SkPaint paint;
         SkAutoTUnref<SkImageFilter> displ(SkImageSource::Create(fCheckerboard));
         // Displacement, with 1 alpha component (which isn't pre-multiplied)
@@ -153,7 +153,7 @@
         return isSmall() ? "displacement_full_small" : "displacement_full_large";
     }
 
-    void onDraw(const int loops, SkCanvas* canvas) override {
+    void onDraw(int loops, SkCanvas* canvas) override {
         SkPaint paint;
         SkAutoTUnref<SkImageFilter> displ(SkImageSource::Create(fCheckerboard));
         // Displacement, with 2 non-alpha components