dm integrity: Remove bi_sector that's only used by commented debug code

drivers/md/dm-integrity.c:1738:13: warning: variable 'bi_sector' set but not used.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=3895


Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>