nfsd: don't kill nfsd_files because of lease break error

An error from break_lease is non-fatal, so we needn't destroy the
nfsd_file in that case. Just put the reference like we normally would
and return the error.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>