LU-8066 lov: fix lov.*.stripeoffset printing

LU-8066 lov: fix lov.*.stripeoffset printing

The move of lov.*.stripeoffset from /proc to /sys in commit 3c900918
reverted the printing of stripeoffset from a signed value to an
unsigned value, which is broken for the common value of "-1".  This
was previously fixed in LU-9611 commit f93276d9.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ib61305ddbf902dd74ac0e16c0c2fe6920052ddf4
Reviewed-on: https://review.whamcloud.com/33019
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>