[BugFix] error path joining of get_design_path util

[yihuajack]

The get_design_path function in utils.py has a bug. To run python3 run_designs.py --regression scripts/config/regression.config spm, it will show error:

Traceback (most recent call last):
File "run_designs.py", line 423, in
cli()
File "/usr/local/lib/python3.6/site-packages/click/core.py", line 1128, in call
return self.main(*args, **kwargs)
File "/usr/local/lib/python3.6/site-packages/click/core.py", line 1053, in main
rv = self.invoke(ctx)
File "/usr/local/lib/python3.6/site-packages/click/core.py", line 1395, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/usr/local/lib/python3.6/site-packages/click/core.py", line 754, in invoke
return __callback(*args, **kwargs)
File "run_designs.py", line 338, in cli
ConfigHandler.gen_base_config(design, base_config_path)
File "/openlane/scripts/config/config.py", line 105, in gen_base_config
copyfile(config_file, base_config_file)
File "/usr/lib64/python3.6/shutil.py", line 120, in copyfile
with open(src, 'rb') as fsrc:
FileNotFoundError: [Errno 2] No such file or directory: '/openlane/./designs/spm/config.tcl'

This is because os.path.join(os.getcwd(), f"./designs/{design}/") is '/openlane/./designs/spm/'.

[donn]

Went ahead and decided to make things more consistent- let's see if anything breaks