FUSE: Fix misunderstanding of KBFSOps.CreateFile/CreateDir return value
FUSE: Fix misunderstanding of KBFSOps.CreateFile/CreateDir return value

The path returned is path of the newly-created child, fix path
updating logic.

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