LU-12361 lov: fix wrong calculated length for fiemap

LU-12361 lov: fix wrong calculated length for fiemap

lov_stripe_intersects() will return a closed interval
[@obd_start, @obd_end], so to calcuate length of interval we need

 @obd_end - @obd_start + 1

rather than

 @obd_end - @obd_start

Wrong extent length will make us return wrong fiemap information.

Change-Id: I30deb17cf5fa80a6d3046098fbac0d3faa01ad1c
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-on: https://review.whamcloud.com/34998
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Gu Zheng <gzheng@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>