Fix NULL as SkColor warning on clang.




git-svn-id: http://skia.googlecode.com/svn/trunk@3582 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/SkGpuDevice.cpp b/src/gpu/SkGpuDevice.cpp
index 9e4a7b6..9113fba 100644
--- a/src/gpu/SkGpuDevice.cpp
+++ b/src/gpu/SkGpuDevice.cpp
@@ -65,7 +65,7 @@
 #define DO_DEFERRED_CLEAR       \
     do {                        \
         if (fNeedClear) {       \
-            this->clear(NULL);  \
+            this->clear(0x0);   \
             fNeedClear = false; \
         }                       \
     } while (false)             \