afsmonitor: Fix multiple NUM_FS_STAT_ENTRIES overflows

If an array is n elements long, accessing element array[n] is an
overflow. Fix various places where we apply loop bounds incorrectly
using the NUM_FS_STAT_ENTRIES constant.

Caught by coverity (#985570, #985571, #985572)

Reviewed-on: http://gerrit.openafs.org/9315
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 4ea1c8440aad6bb6dc9cdb598b5708c685603219)

Change-Id: I028fcb13716ba60266635a1f04f2dda083cba1a3
Reviewed-on: http://gerrit.openafs.org/11028
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>