use list intialization for AsynSubgraph::next_buffer_handle_
Hi @yijie-yang Can you please review this PR ? Thank you!
List intialization fixes error of `copying member subobject of type 'std::atomic<TfLiteBufferHandle>' (aka 'atomic<int>') invokes deleted constructor` at `std::atomic<TfLiteBufferHandle> next_buffer_handle_ = 0;` at `tensorflow/lite/core/async/async_subgraph.h` line:165