[dnnlowp] reduce num of test cases to avoid time out (#64935)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64935
As title
Test Plan: CI
Reviewed By: dskhudia
Differential Revision: D30889157
fbshipit-source-id: 316c808806b084bd2e44c56e1cdb61adf2369a9d
