[usb] Leave port enabled after a failed device registration

A failure in device registration (e.g. due to a device with malformed
descriptors) will currently result in the port being disabled as part
of the error path.  This in turn causes the hardware to detect the
device as newly connected, leading to an endless loop of failed device
registrations.

Fix by leaving the port enabled in the case of a registration failure.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/bus/usb.c

@@ -1615,7 +1615,9 @@ static int register_usb ( struct usb_device *usb ) {
 	usb->host->close ( usb );
  err_open:
  err_speed:
-	hub->driver->disable ( hub, port );
+	/* Leave port enabled on failure, to avoid an endless loop of
+	 * failed device registrations.
+	 */
  err_enable:
 	list_del ( &usb->list );
 	port->usb = NULL;