NFSv4: Remove bogus "struct nfs_client" argument from decode_ace()

We shouldn't need to force callers to carry an unused argument.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>