USB: usbip: missing lock in stub down

Missing lock in sysfs operation when we want to close the connection in order
to check the status and send the down event in a safe way.

Signed-off-by: Jose Ignacio Tornos Martinez <[e-mail]>
Reviewed-by: Shuah Khan <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/usbip/stub_dev.c

···
 	} else {
 		dev_info(dev, "stub down\n");
 
+		mutex_lock(&sdev->ud.sysfs_lock);
+
 		spin_lock_irq(&sdev->ud.lock);
 		if (sdev->ud.status != SDEV_ST_USED)
 			goto err;