NFS: Always use the open stateid when checking for expired opens

If we are reading through a delegation, and the delegation is OK then
state->stateid will still point to a delegation stateid and not an open
stateid.

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>