removed the "bits" attribute from android_native_buffer_t.

"bits" can never be trusted now that we need to call lock() on the handle to get the virtual address of the buffer.
diff --git a/include/ui/Surface.h b/include/ui/Surface.h
index 6eb06ae..ce50719 100644
--- a/include/ui/Surface.h
+++ b/include/ui/Surface.h
@@ -54,8 +54,8 @@
         return handle;
     }
     
-    status_t lock(uint32_t usage);
-    status_t lock(uint32_t usage, const Rect& rect);
+    status_t lock(uint32_t usage, void** vaddr);
+    status_t lock(uint32_t usage, const Rect& rect, void** vaddr);
     status_t unlock();
 
 protected: