just zero flags

This memset() zeroes more than is really needed.
All these fields will be overwritten eventually,
unless we early return where none of them are used.

Change-Id: Ibb75ae8853eab81251a8995bb9d681689187e727
Reviewed-on: https://skia-review.googlesource.com/153262
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
diff --git a/src/core/SkColorSpaceXformSteps.h b/src/core/SkColorSpaceXformSteps.h
index adb92d8..afc7f45 100644
--- a/src/core/SkColorSpaceXformSteps.h
+++ b/src/core/SkColorSpaceXformSteps.h
@@ -15,11 +15,11 @@
 
 struct SkColorSpaceXformSteps {
     struct Flags {
-        bool unpremul;
-        bool linearize;
-        bool gamut_transform;
-        bool encode;
-        bool premul;
+        bool unpremul         = false;
+        bool linearize        = false;
+        bool gamut_transform  = false;
+        bool encode           = false;
+        bool premul           = false;
 
         uint32_t mask() const {
             return (unpremul        ?  1 : 0)