nfs: remove incorrect usage of nfs4 compound response hdr.status

3 call sites look at hdr.status before returning success.
hdr.status must be zero in this case so there's no point in this.

Currently, hdr.status is correctly processed at decode_op_hdr time
if the op status cannot be decoded.

Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>