tmpfs does not implement ->get_acl method, overlayfs
need to get its cached acls in permission check when
lower or upper fs is tmpfs.
CC: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Xiong Zhou <xzhou@redhat.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>