NFSv4.1: Fix a regression in DELEGRETURN

We don't want to call nfs4_free_revoked_stateid() in the case where
the delegreturn was successful.

Reported-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>