git-cl: Fix Change object construction for git-cl split

Changelist.GetChange signature was changed in
https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2038050

Bug: 1042324, 1054880
Change-Id: I6ba63e7f2f6c13bd8e8bef4e76cd66ee0525bba2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2067623
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

split_cl.py

@@ -340,7 +340,7 @@ def SplitCl(description_file, comment_file, changelist, cmd_upload, dry_run,
     EnsureInGitRepository()
 
     cl = changelist()
-    change = cl.GetChange(cl.GetCommonAncestorWithUpstream(), None)
+    change = cl.GetChange(cl.GetCommonAncestorWithUpstream())
     files = change.AffectedFiles()
 
     if not files: