GFS2: fsck.gfs2 reported statfs error after gfs2_grow

When you do gfs2_grow it failed to take the very last
rgrp into account when adding up the new free space due
to an off-by-one error.  It was not reading the last
rgrp from the rindex because of a check for "<=" that
should have been "<".  Therefore, fsck.gfs2 was finding
(and fixing) an error with the system statfs file.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>