sync: fix recursive fetching
sync: fix recursive fetching

Commit b2fa30a2b891b22c173c960a67bf38ccbba8de1b ("sync: switch network
fetch to multiprocessing") accidentally changed the variable passed to
the 2nd fetch call from |missing| to |to_fetch| due to a copy & paste
of the earlier changed logic.  Undo that to fix git submodule fetching.

Bug: https://crbug.com/gerrit/14489
Change-Id: I627954f80fd2e80d9d5809b530aa6b0ef9260abb
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/305262
Reviewed-by: Raman Tenneti <66788d848ab03efc83371cd4b586a3110f9172ef@google.com>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@google.com>

couchbasedeps/git-repo,couchbasedeps/git-repo,lewixliu/git-repo,lewixliu/git-repo,GerritCodeReview/git-repo,GerritCodeReview/git-repo