Fixes CI error:
Traceback (most recent call last):
  File "/builds/nirbheek/cerbero/cerbero/build/oven.py", line 461, in _cook_recipe_step
    ret = stepfunc()
  File "/builds/nirbheek/cerbero/cerbero/build/recipe.py", line 93, in wrapped
    stepfunc()
  File "/builds/nirbheek/cerbero/recipes/libdca.recipe", line 34, in post_install
    os.symlink(src, os.path.join(self.config.prefix, dest))

FileExistsError: [Errno 17] File exists: 'lib/libdts.a' -> '/builds/nirbheek/cerbero/cerbero-build/dist/mingw_x86_64/libdca.a'
Part-of: <!618>