Fix for Sk4f Ubuntu compile warning

src/core/SkPixmap.cpp

Index: src/core/SkPixmap.cpp
diff --git a/src/core/SkPixmap.cpp b/src/core/SkPixmap.cpp
index a5e474b6d4d8c0ec4658c82b00af005bfabb7b58..bd551ed9d3dd09a2a2c51ddc05cbbdb31c4b9b1f 100644
--- a/src/core/SkPixmap.cpp
+++ b/src/core/SkPixmap.cpp
@@ -226,7 +226,7 @@ bool SkPixmap::erase(const SkColor4f& origColor, const SkIRect* subset) const {
     if (kRGBA_F16_SkColorType != pm.colorType()) {
         Sk4f c4 = Sk4f::Load(color.vec());
         SkColor c;
-        (c4 * Sk4f(255) + Sk4f(0.5f)).store(&c);
+        SkNx_cast<uint8_t>(c4 * Sk4f(255) + Sk4f(0.5f)).store(&c);
         return pm.erase(c);
     }