Fix quantized mean operator in QNNPACK backend (#59761)
Summary:
cc: kimishpatel
Fixes https://github.com/pytorch/pytorch/issues/58668
Test it with `pytest -k test_quantized_mean test/test_quantization.py` or `buck test //caffe2/test:quantization -- test_quantized_mean`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/59761
Reviewed By: bdhirsh
Differential Revision: D29013271
Pulled By: kimishpatel
fbshipit-source-id: 020956fb63bd5078856ca17b137be016d3fc29b8
