bugfix for typo in skpdiff tool

tools/skpdiff/SkDiffContext.cpp

Index: tools/skpdiff/SkDiffContext.cpp
diff --git a/tools/skpdiff/SkDiffContext.cpp b/tools/skpdiff/SkDiffContext.cpp
index a1cc665dc2a150870650c40c8952ee4ade9906b5..df1c93dfd29775db6b58f501b21b986617302171 100644
--- a/tools/skpdiff/SkDiffContext.cpp
+++ b/tools/skpdiff/SkDiffContext.cpp
@@ -108,7 +108,7 @@ void SkDiffContext::addDiff(const char* baselinePath, const char* testPath) {
 
         if (!differ->diff(&baselineBitmap, &testBitmap, alphaMaskPending, &diffData.fResult)) {
             // if the diff failed record -1 as the result
-            diffData.fResult = -1;
+            diffData.fResult.result = -1;
             continue;
         }