Improve naive SkColorXform to half floats

src/effects/gradients/Sk4fGradientPriv.h

Index: src/effects/gradients/Sk4fGradientPriv.h
diff --git a/src/effects/gradients/Sk4fGradientPriv.h b/src/effects/gradients/Sk4fGradientPriv.h
index 68e95a63d9ff7dda846dc7eecc3a8c71967f23b1..9745119fd4a23659adc8b60984d3da956dce5b5b 100644
--- a/src/effects/gradients/Sk4fGradientPriv.h
+++ b/src/effects/gradients/Sk4fGradientPriv.h
@@ -143,11 +143,13 @@ struct DstTraits<DstType::F16, premul> {
     }
 
     static void store(const Sk4f& c, Type* dst) {
-        *dst = SkFloatToHalf_finite(PM::apply(c));
+        SkFloatToHalf_finite(PM::apply(c)).store(dst);
     }
 
     static void store(const Sk4f& c, Type* dst, int n) {
-        sk_memset64(dst, SkFloatToHalf_finite(PM::apply(c)), n);
+        uint64_t color;
+        SkFloatToHalf_finite(PM::apply(c)).store(&color);
+        sk_memset64(dst, color, n);
     }
 
     static void store4x(const Sk4f& c0, const Sk4f& c1,