fix printf warning in dumpcanvas

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3040

Change-Id: I850609e499a670cda0fd09941345fe221fbeeffb
Reviewed-on: https://skia-review.googlesource.com/3040
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/src/utils/SkDumpCanvas.cpp b/src/utils/SkDumpCanvas.cpp
index 68bd13e..eda23b7 100644
--- a/src/utils/SkDumpCanvas.cpp
+++ b/src/utils/SkDumpCanvas.cpp
@@ -210,7 +210,7 @@
             str.appendf(" alpha:0x%02X", paint->getAlpha());
         }
         if (!paint->isSrcOver()) {
-            str.appendf(" blendmode:%d", paint->getBlendMode());
+            str.appendf(" blendmode:%d", (int)paint->getBlendMode());
         }
     }
     this->dump(kSave_Verb, paint, str.c_str());