Fix some clang warnings with -Wmissing-braces in ANGLE.

Clang warns if there are missing braces around a subobject
initializer. The most common idiom that triggers this is:
STRUCT s = {0};
which can be more simply written as:
STRUCT s = {};

BUG=505297

Change-Id: Ib4513ee195d43e7c4a4a2f46c328866f0023a2a5
Reviewed-on: https://chromium-review.googlesource.com/282921
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Tested-by: Kenneth Russell <kbr@chromium.org>
diff --git a/src/libANGLE/renderer/d3d/ProgramD3D.cpp b/src/libANGLE/renderer/d3d/ProgramD3D.cpp
index 617080b..5374613 100644
--- a/src/libANGLE/renderer/d3d/ProgramD3D.cpp
+++ b/src/libANGLE/renderer/d3d/ProgramD3D.cpp
@@ -1061,7 +1061,7 @@
     mShaderVersion = vertexShaderD3D->getShaderVersion();
 
     // Map the varyings to the register file
-    VaryingPacking packing = { NULL };
+    VaryingPacking packing = {};
     *registers = mDynamicHLSL->packVaryings(infoLog, packing, fragmentShaderD3D, vertexShaderD3D, transformFeedbackVaryings);
 
     if (*registers < 0)