Update link to qnnpack in quantization doc. (#66226)
Summary:
The old repo has been archived.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66226
Reviewed By: vkuzo
Differential Revision: D31534712
Pulled By: ezyang
fbshipit-source-id: 4d7f070c8547aeb25464c72b25ed21f209821bc2
