change flattenable factory to return sk_sp

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1855733002

Review URL: https://codereview.chromium.org/1855733002
diff --git a/src/effects/SkDashPathEffect.cpp b/src/effects/SkDashPathEffect.cpp
index 51bf548..90af32e 100644
--- a/src/effects/SkDashPathEffect.cpp
+++ b/src/effects/SkDashPathEffect.cpp
@@ -360,12 +360,12 @@
     buffer.writeScalarArray(fIntervals, fCount);
 }
 
-SkFlattenable* SkDashPathEffect::CreateProc(SkReadBuffer& buffer) {
+sk_sp<SkFlattenable> SkDashPathEffect::CreateProc(SkReadBuffer& buffer) {
     const SkScalar phase = buffer.readScalar();
     uint32_t count = buffer.getArrayCount();
     SkAutoSTArray<32, SkScalar> intervals(count);
     if (buffer.readScalarArray(intervals.get(), count)) {
-        return Make(intervals.get(), SkToInt(count), phase).release();
+        return Make(intervals.get(), SkToInt(count), phase);
     }
     return nullptr;
 }