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: bd8b82042269 ("usbip: vudc synchronize sysfs code paths")
Reported-by: Hulk Robot <[e-mail]>
Acked-by: Shuah Khan <[e-mail]>
Signed-off-by: Ye Bin <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/usbip/vudc_sysfs.c

···
 		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;
 		}