usbip: vudc: fix missing unlock on error in usbip_sockfd_store()

Add the missing unlock before return from function usbip_sockfd_store()
in the error handling case.

Fixes: bd8b8204 ("usbip: vudc synchronize sysfs code paths")
Reported-by: Hulk Robot <hulkci@huawei.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Ye Bin <yebin10@huawei.com>
Link: https://lore.kernel.org/r/20210408112305.1022247-1-yebin10@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/usbip/vudc_sysfs.c

@@ -156,12 +156,14 @@ static ssize_t usbip_sockfd_store(struct device *dev,
 		tcp_rx = kthread_create(&v_rx_loop, &udc->ud, "vudc_rx");
 		if (IS_ERR(tcp_rx)) {
 			sockfd_put(socket);
+			mutex_unlock(&udc->ud.sysfs_lock);
 			return -EINVAL;
 		}
 		tcp_tx = kthread_create(&v_tx_loop, &udc->ud, "vudc_tx");
 		if (IS_ERR(tcp_tx)) {
 			kthread_stop(tcp_rx);
 			sockfd_put(socket);
+			mutex_unlock(&udc->ud.sysfs_lock);
 			return -EINVAL;
 		}