nfsstat: fix a bug in diff_stats()

	Fix a bug in diff_stats() that causes false-positives in
has_stats(), which can result in a bunch of zeros being displayed instead
of suppressed as intended.

Signed-off-by: David M. Richter <richterd@citi.umich.edu>
Signed-off-by: Neil Brown <neilb@suse.de>