Fix valgrind bug in Porter Duff LCD.

BUG=skia:

Review URL: https://codereview.chromium.org/1135283002
diff --git a/src/gpu/effects/GrPorterDuffXferProcessor.cpp b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
index c1db0ca..8b92eba 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.cpp
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
@@ -563,7 +563,7 @@
 
 void PDLCDXferProcessor::onGetGLProcessorKey(const GrGLSLCaps& caps,
                                              GrProcessorKeyBuilder* b) const {
-    GLPorterDuffXferProcessor::GenKey(*this, caps, b);
+    GLPDLCDXferProcessor::GenKey(*this, caps, b);
 }
 
 GrGLXferProcessor* PDLCDXferProcessor::createGLInstance() const {