smb: client: prevent new fids from being removed by laundromat

Check if @cfid->time is set in laundromat so we guarantee that only
fully cached fids will be selected for removal.  While we're at it,
add missing locks to protect access of @cfid fields in order to avoid
races with open_cached_dir() and cfids_laundromat_worker(),
respectively.

Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>