SCSI: use the proper semaphore to protect the class lists

SCSI was using the incorrect lock to protect walking the list of all
devices in the class.  This patch fixes this.

Cc: James Bottomley <James.Bottomley@SteelEye.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/scsi/hosts.c

@@ -435,7 +435,7 @@ struct Scsi_Host *scsi_host_lookup(unsigned short hostnum)
 	struct class_device *cdev;
 	struct Scsi_Host *shost = ERR_PTR(-ENXIO), *p;
 
-	down_read(&class->subsys.rwsem);
+	down(&class->sem);
 	list_for_each_entry(cdev, &class->children, node) {
 		p = class_to_shost(cdev);
 		if (p->host_no == hostnum) {
@@ -443,7 +443,7 @@ struct Scsi_Host *scsi_host_lookup(unsigned short hostnum)
 			break;
 		}
 	}
-	up_read(&class->subsys.rwsem);
+	up(&class->sem);
 
 	return shost;
 }