fix warning from scalar --> int32 conversion

BUG=

Review URL: https://codereview.appspot.com/7065050

git-svn-id: http://skia.googlecode.com/svn/trunk@7061 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/effects/SkMatrixConvolutionImageFilter.cpp b/src/effects/SkMatrixConvolutionImageFilter.cpp
index b5188b3..74a1163 100644
--- a/src/effects/SkMatrixConvolutionImageFilter.cpp
+++ b/src/effects/SkMatrixConvolutionImageFilter.cpp
@@ -43,7 +43,7 @@
     fKernelSize.fHeight = buffer.readInt();
     uint32_t size = fKernelSize.fWidth * fKernelSize.fHeight;
     fKernel = SkNEW_ARRAY(SkScalar, size);
-    uint32_t readSize = buffer.readScalarArray(fKernel);
+    SkDEBUGCODE(uint32_t readSize = )buffer.readScalarArray(fKernel);
     SkASSERT(readSize == size);
     fGain = buffer.readScalar();
     fBias = buffer.readScalar();