firewire: fix ioctl() return code

Reported by Jay Fenlason:  ioctl() did not return as intended
  - the size of data read into ioctl_send_request,
  - the number of datagrams enqueued by ioctl_queue_iso.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/fw-cdev.c

@@ -913,7 +913,7 @@ dispatch_ioctl(struct client *client, unsigned int cmd, void __user *arg)
 			return -EFAULT;
 	}
 
-	return 0;
+	return retval;
 }
 
 static long