Also sync submodule in the Dockerfile (#35423)
Summary:
Sometimes submodule URL may have changed between commits. Let Dockerfile
also sync submodules before updating.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35423
Differential Revision: D20658464
Pulled By: ngimel
fbshipit-source-id: 9c101338437f9e86432d3502766858fa5156a800
