explicitly provide memory format when calling to clone() at SobolEngineOps.cpp
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/28662
Test Plan: Imported from OSS
Differential Revision: D18333374
Pulled By: ifedan
fbshipit-source-id: c8e18e9937b373daba0ead819622350b693c4bfa
