nfsd_sync* return an errno, which usually needs to be converted to an errno,
sometimes immediately, sometimes a little later.

Also, nfsd_setattr returns an nfserr which SHOULDN'T be converted from
an errno (because it isn't one).

Also some tidyups of the form:
  err = XX
  err = nfserrno(err)
and
  err = XX
  if (err)
      err = nfserrno(err)
become
  err = nfserrno(XX)
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>