Fix bug in filterSpan4f - read the source, rather than the dest

src/core/SkColorFilter.cpp

Index: src/core/SkColorFilter.cpp
diff --git a/src/core/SkColorFilter.cpp b/src/core/SkColorFilter.cpp
index 9470766732146c81723c4bea7a0c3d76f29903fa..8a37e1b56c022533243d2bcae0c92697840b5bbd 100644
--- a/src/core/SkColorFilter.cpp
+++ b/src/core/SkColorFilter.cpp
@@ -37,19 +37,20 @@ sk_sp<GrFragmentProcessor> SkColorFilter::asFragmentProcessor(GrContext*) const
 }
 #endif
 
-void SkColorFilter::filterSpan4f(const SkPM4f[], int count, SkPM4f span[]) const {
+void SkColorFilter::filterSpan4f(const SkPM4f src[], int count, SkPM4f result[]) const {
     const int N = 128;
     SkPMColor tmp[N];
     while (count > 0) {
         int n = SkTMin(count, N);
         for (int i = 0; i < n; ++i) {
-            SkNx_cast<uint8_t>(Sk4f::Load(span[i].fVec) * Sk4f(255) + Sk4f(0.5f)).store(&tmp[i]);
+            SkNx_cast<uint8_t>(Sk4f::Load(src[i].fVec) * Sk4f(255) + Sk4f(0.5f)).store(&tmp[i]);
         }
         this->filterSpan(tmp, n, tmp);
         for (int i = 0; i < n; ++i) {
-            span[i] = SkPM4f::FromPMColor(tmp[i]);
+            result[i] = SkPM4f::FromPMColor(tmp[i]);
         }
-        span += n;
+        src += n;
+        result += n;
         count -= n;
     }
 }