graphics: sideband streams are not buffers

We should call native_handle_clone instead of IMapper::importBuffer
on sideband stream handles.

Bug: 63707399
Test: manual
Change-Id: Ie07e50f6bb771f3c7a69d29e36f60b149dc6af95
diff --git a/graphics/composer/2.1/default/ComposerClient.h b/graphics/composer/2.1/default/ComposerClient.h
index ee825fe..fc5c223 100644
--- a/graphics/composer/2.1/default/ComposerClient.h
+++ b/graphics/composer/2.1/default/ComposerClient.h
@@ -110,6 +110,7 @@
 protected:
     struct LayerBuffers {
         std::vector<BufferCacheEntry> Buffers;
+        // the handle is a sideband stream handle, not a buffer handle
         BufferCacheEntry SidebandStream;
     };