nfsd4: fix setlease error return

This actually makes a difference in the 4.1 case, since we use the
status to decide what reason to give the client for the delegation
refusal (see nfsd4_open_deleg_none_ext), and in theory a client might
choose suboptimal behavior if we give the wrong answer.

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