tools.check_patch: Use working dir for project checking

Hi guys, as we have more and more submodules, we should reconsider the way check_patch works. This solution uses current dir to find the project you want to check.

Please keep in mind that this is only a simple modification without much testing only to demonstrate how I'd expect check_patch to work. Please let me know, what do you think and then I'll test and fix the possible bugs before this is applied.

Kind regards,
Lukáš