Fix for Sk4f Ubuntu compile warning

src/core/SkPixmap.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkColorPriv.h"
 #include "SkConfig8888.h"
 #include "SkData.h"
@@ skipping 208 matching lines @@
         }
     } else {
         pm = *this;
     }
 
     const SkColor4f color = origColor.pin();
 
     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);
     }
 
     const uint64_t half4 = color.premul().toF16();
     for (int y = 0; y < pm.height(); ++y) {
         sk_memset64(pm.writable_addr64(0, y), half4, pm.width());
     }
     return true;
 }
 
@@ skipping 26 matching lines @@
 
     SkPaint paint;
     paint.setFilterQuality(quality);
     paint.setXfermodeMode(SkXfermode::kSrc_Mode);
     surface->getCanvas()->drawBitmapRect(bitmap, SkRect::MakeIWH(dst.width(), dst.height()),
                                          &paint);
     return true;
 }
 
 //////////////////////////////////////////////////////////////////////////////////////////////////