scsi: usb-storage: Use scsi_cmd_to_rq() instead of scsi_cmnd.request

Prepare for removal of the request pointer by using scsi_cmd_to_rq()
instead. This patch does not change any functionality.

Link: https://lore.kernel.org/r/20210809230355.8186-52-bvanassche@acm.orgAcked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/usb/storage/transport.c

@@ -551,7 +551,7 @@ static void last_sector_hacks(struct us_data *us, struct scsi_cmnd *srb)
 	/* Did this command access the last sector? */
 	sector = (srb->cmnd[2] << 24) | (srb->cmnd[3] << 16) |
 			(srb->cmnd[4] << 8) | (srb->cmnd[5]);
-	disk = srb->request->rq_disk;
+	disk = scsi_cmd_to_rq(srb)->rq_disk;
 	if (!disk)
 		goto done;
 	sdkp = scsi_disk(disk);