NFSv4: Return the delegation if the server returns NFS4ERR_OPENMODE

If a setattr() fails because of an NFS4ERR_OPENMODE error, it is
probably due to us holding a read delegation. Ensure that the
recovery routines return that delegation in this case.

Reported-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@vger.kernel.org