Add support for user-allocated buffers from the C++ API.

Bug: 7256604
Change-Id: Ia5d458ebadfd893e41130f90a1650258280a41cd
diff --git a/rsAllocation.h b/rsAllocation.h
index b552ca3..5ee9afb 100644
--- a/rsAllocation.h
+++ b/rsAllocation.h
@@ -61,7 +61,7 @@
             bool hasMipmaps;
             bool hasFaces;
             bool hasReferences;
-            void * unused_01;
+            void * userProvidedPtr;
             int32_t surfaceTextureID;
             ANativeWindow *wndSurface;
             SurfaceTexture *surfaceTexture;