update windows port

git-svn-id: http://skia.googlecode.com/svn/trunk@461 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/effects/SkGradientShader.cpp b/src/effects/SkGradientShader.cpp
index f085017..5a3a80a 100644
--- a/src/effects/SkGradientShader.cpp
+++ b/src/effects/SkGradientShader.cpp
@@ -490,7 +490,7 @@
 }
 
 static inline U16CPU bitsTo16(unsigned x, const unsigned bits) {
-    SkASSERT(x < (1 << bits));
+    SkASSERT(x < (1U << bits));
     if (6 == bits) {
         return (x << 10) | (x << 4) | (x >> 2);
     }