Expose mBufferId for GraphicBuffer

Bug: 118844974
Test: GraphicBuffer_test
Change-Id: I75a58b21e9943ffed9219a37e0d05c6697232bf4
diff --git a/libs/ui/GraphicBuffer.cpp b/libs/ui/GraphicBuffer.cpp
index e606e26..f408fcb 100644
--- a/libs/ui/GraphicBuffer.cpp
+++ b/libs/ui/GraphicBuffer.cpp
@@ -104,6 +104,7 @@
                                 buffer->desc().width, buffer->desc().height,
                                 static_cast<PixelFormat>(buffer->desc().format),
                                 buffer->desc().layers, buffer->desc().usage, buffer->desc().stride);
+    mBufferId = buffer->id();
     mBufferHubBuffer = std::move(buffer);
 }
 #endif // LIBUI_IN_VNDK