ovl: use cached acl on underlying layer

ovl: use cached acl on underlying layer

Instead of calling ->get_acl() directly, use get_acl() to get the cached
value.

We will have the acl cached on the underlying inode anyway, because we do
permission checking on the both the overlay and the underlying fs.

So, since we already have double caching, this improves performance without
any cost.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Orabug: 26401569

(backport upstream commit 5201dc449e4b6b6d7e92f7f974269b11681f98b5)

Signed-off-by: Shan Hai <shan.hai@oracle.com>
Reviewed-by: Somasundaram Krishnasamy <somasundaram.krishnasamy@oracle.com>