Add missing file to BUILD.bazel (#40536)
Summary:
Add `int8_gen_quant_params.cc` added by
https://github.com/pytorch/pytorch/pull/40494/ to bazel build rules
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40536
Reviewed By: mruberry
Differential Revision: D22219595
Pulled By: malfet
fbshipit-source-id: 2875a0b9c55bad2b052a898661b96eab490f6451
