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/libs/surfaceflinger/LayerBitmap.cpp b/libs/surfaceflinger/LayerBitmap.cpp
index 38d4bcf..765d90b 100644
--- a/libs/surfaceflinger/LayerBitmap.cpp
+++ b/libs/surfaceflinger/LayerBitmap.cpp
@@ -116,7 +116,8 @@
 
 status_t Buffer::lock(GGLSurface* sur, uint32_t usage) 
 {
-    status_t res = SurfaceBuffer::lock(usage);
+    void* vaddr;
+    status_t res = SurfaceBuffer::lock(usage, &vaddr);
     if (res == NO_ERROR && sur) {
         sur->version = sizeof(GGLSurface);
         sur->width = width;
@@ -124,7 +125,7 @@
         sur->stride = stride;
         sur->format = format;
         sur->vstride = mVStride;
-        sur->data = static_cast<GGLubyte*>(bits);
+        sur->data = static_cast<GGLubyte*>(vaddr);
     }
     return res;
 }