scsi: restructure command initialization for TYPE_FS requests

We should call the device handler prep_fn for all TYPE_FS requests,
not just simple read/write calls that are handled by the disk driver.

Restructure the common I/O code to call the prep_fn handler and zero
out the CDB, and just leave the call to scsi_init_io to the ULDs.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>

drivers/scsi/sr.c

@@ -385,10 +385,9 @@ static int sr_init_command(struct scsi_cmnd *SCpnt)
 	int block = 0, this_count, s_size;
 	struct scsi_cd *cd;
 	struct request *rq = SCpnt->request;
-	struct scsi_device *sdp = SCpnt->device;
 	int ret;
 
-	ret = scsi_setup_fs_cmnd(sdp, rq);
+	ret = scsi_init_io(SCpnt, GFP_ATOMIC);
 	if (ret != BLKPREP_OK)
 		goto out;
 	SCpnt = rq->special;