[Quant] Fix setting fixed qparams for inner LSTM ops (#95537)
Summary: The existing util function did not quantize all inner
ops in the quantizable LSTM module, resulting in the error
"Could not run X with arguments from the 'QuantizedCPU' backend."
This commit fixes this by ensuring that all the other ops whose
qparams were not specifically configured are still quantized as
before, as in `torch.ao.nn.quantizable.LSTM.from_float`.
Test Plan: This commit also adds an additional check in the test
to ensure that the final converted model is in fact quantized,
in addition to just checking the qparams in the observers have
the right values.
python test/test_quantization.py TestQuantizeFx.test_static_lstm_with_custom_fixed_qparams
Reviewers: vkuzo
Subscribers: vkuzo, supriyar
Pull Request resolved: https://github.com/pytorch/pytorch/pull/95537
Approved by: https://github.com/vkuzo
