[libata] use scsi host lock

In 2.4 we release io_request_lock and take our own per-host lock,
in the ->queuecommand() hook.  In 2.6, the SCSI layer provides a
useful to simply use the lock we already have, via scsi_assign_lock().

drivers/scsi/libata-core.c

@@ -2864,6 +2864,7 @@ static void ata_host_init(struct ata_port *ap, struct Scsi_Host *host,
 	host->unique_id = ata_unique_id++;
 	host->max_cmd_len = 12;
 	scsi_set_device(host, &ent->pdev->dev);
+	scsi_assign_lock(host, &host_set->lock);
 
 	ap->flags = ATA_FLAG_PORT_DISABLED;
 	ap->id = host->unique_id;

drivers/scsi/libata-scsi.c

@@ -970,9 +970,6 @@ int ata_scsi_queuecmd(struct scsi_cmnd *cmd, void (*done)(struct scsi_cmnd *))
 					   0;
 #endif
 
-	/* Note: spin_lock_irqsave is held by caller... */
-	spin_unlock(cmd->device->host->host_lock);
-
 	ap = (struct ata_port *) &cmd->device->host->hostdata[0];
 
 	DPRINTK("CDB (%u:%d,%d,%d) %02x %02x %02x %02x %02x %02x %02x %02x %02x\n",
@@ -990,8 +987,6 @@ int ata_scsi_queuecmd(struct scsi_cmnd *cmd, void (*done)(struct scsi_cmnd *))
 		goto out;
 	}
 
-	spin_lock(&ap->host_set->lock);
-
 	dev = &ap->device[cmd->device->id];
 
 	if (!ata_dev_present(dev)) {
@@ -1105,10 +1100,8 @@ int ata_scsi_queuecmd(struct scsi_cmnd *cmd, void (*done)(struct scsi_cmnd *))
 			break;
 	}
 
-out_unlock:
-	spin_unlock(&ap->host_set->lock);
+out_unlock:		/* I will kill this soon... reduces 2.4 diff */
 out:
-	spin_lock(cmd->device->host->host_lock);
 	return 0;
 }