block: use bvec_virt in bio_integrity_{process,free}

Use the bvec_virt helper to clean up the bio integrity processing a
little bit.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@kernel.org>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20210804095634.460779-3-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>