cifs: Do not use tcon->cfid directly, use the cfid we get from open_cached_dir

They are the same right now but tcon-> will later point to a different
type of struct containing a list of cfids.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>