Convert SkAutoTUnref<SkData> to sk_sp<SkData>.

With the move from SkData::NewXXX to SkData::MakeXXX most
SkAutoTUnref<SkData> were changed to sk_sp<SkData>. However,
there are still a few SkAutoTUnref<SkData> around, so clean
them up.

Review-Url: https://codereview.chromium.org/2212493002
diff --git a/src/ports/SkImageGeneratorCG.h b/src/ports/SkImageGeneratorCG.h
index 53102ea..baf3669 100644
--- a/src/ports/SkImageGeneratorCG.h
+++ b/src/ports/SkImageGeneratorCG.h
@@ -35,7 +35,7 @@
     SkImageGeneratorCG(const SkImageInfo& info, const void* imageSrc, SkData* data);
 
     SkAutoTCallVProc<const void, CFRelease> fImageSrc;
-    SkAutoTUnref<SkData>                    fData;
+    sk_sp<SkData>                           fData;
 
     typedef SkImageGenerator INHERITED;
 };