[git-cache] Fix path splitting.

Bug:1372658
Change-Id: I83627ecc8cee754a1830a9c4453c59bd9c01d728
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3946647
Auto-Submit: Joanna Wang <jojwang@chromium.org>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>

git_cache.py

@@ -518,7 +518,7 @@ class Mirror(object):
     # before we upload to GS.
     # See crbug.com/1370443; keep this check until root cause is found.
     recursed_dir = os.path.join(self.mirror_path,
-                                self.mirror_path.split(os.path)[-1])
+                                self.mirror_path.split(os.path.sep)[-1])
     if os.path.exists(recursed_dir):
       self.print('Deleting unexpected directory: %s' % recursed_dir)
       os.remove(recursed_dir)