folder_branch_ops: don't re-declare new error in `for` loop
folder_branch_ops: don't re-declare new error in `for` loop

It's used in a defer, and needs to be the same as the function's
overall error.

Issue: KBFS-2076

keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/kbfs,keybase/kbfs,keybase/client,keybase/kbfs