sd: use bvec_virt

Use bvec_virt instead of open coding it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20210804095634.460779-11-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/scsi/sd.c

@@ -886,7 +886,7 @@ static blk_status_t sd_setup_unmap_cmnd(struct scsi_cmnd *cmd)
 	cmd->cmnd[0] = UNMAP;
 	cmd->cmnd[8] = 24;
 
-	buf = page_address(rq->special_vec.bv_page);
+	buf = bvec_virt(&rq->special_vec);
 	put_unaligned_be16(6 + 16, &buf[0]);
 	put_unaligned_be16(16, &buf[2]);
 	put_unaligned_be64(lba, &buf[8]);