nfsd: fix setting of NFS4_OO_CONFIRMED in nfsd4_open

In the NFS4_OPEN_CLAIM_PREVIOUS case, we should only mark it confirmed
if the nfs4_check_open_reclaim check succeeds.

In the NFS4_OPEN_CLAIM_DELEG_PREV_FH and NFS4_OPEN_CLAIM_DELEGATE_PREV
cases, I see no point in declaring the openowner confirmed when the
operation is going to fail anyway, and doing so might allow the client
to game things such that it wouldn't need to confirm a subsequent open
with the same owner.

Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>