Fixed remaining clang compiler warnings

https://codereview.appspot.com/6865053/



git-svn-id: http://skia.googlecode.com/svn/trunk@6646 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/tilemodes.cpp b/gm/tilemodes.cpp
index f2fbe77..ab4ea0a 100644
--- a/gm/tilemodes.cpp
+++ b/gm/tilemodes.cpp
@@ -170,6 +170,8 @@
         case 2:
             return SkGradientShader::CreateSweep(center.fX, center.fY, colors, NULL, SK_ARRAY_COUNT(colors));
     }
+
+    return NULL;
 }
 
 static SkShader* make_radial(SkShader::TileMode tx, SkShader::TileMode ty) {