NFSv4.x: Fix NFS4ERR_RETRY_UNCACHED_REP in nfs4_callback_sequence

We need to initialize cb_sequenceres information when reporting a
NFS4ERR_RETRY_UNCACHED_REP error, since that will apply to the
next operation, not to the CB_SEQUENCE itself.

Reported-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>