Fix GLSL error on Android.

BUG=skia:
TBR=bsalomon
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1053873002
diff --git a/src/gpu/effects/GrMatrixConvolutionEffect.cpp b/src/gpu/effects/GrMatrixConvolutionEffect.cpp
index f6b99ef..0b0a8af 100644
--- a/src/gpu/effects/GrMatrixConvolutionEffect.cpp
+++ b/src/gpu/effects/GrMatrixConvolutionEffect.cpp
@@ -90,7 +90,7 @@
             fDomain.sampleTexture(fsBuilder, domain, "c", coord, samplers[0]);
             if (!fConvolveAlpha) {
                 fsBuilder->codeAppend("c.rgb /= c.a;");
-                fsBuilder->codeAppend("c.rgb = clamp(c.rgb, 0, 1);");
+                fsBuilder->codeAppend("c.rgb = clamp(c.rgb, 0.0, 1.0);");
             }
             fsBuilder->codeAppend("sum += c * k;");
         }