nfsd: replace Jeff by Chuck as nfsd co-maintainer

Jeff's picking up more responsibilities elsewhere, and Chuck's agreed to
take over.

For now, as before, nothing's changing day-to-day, but I want to have a
co-maintainer if only for bus factor.

Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>