staging: pi433: fix error return code in pi433_probe()

Fix to return a negative error code from the kthread_run() error
handling case instead of 0, as done elsewhere in this function.
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/pi433/pi433_if.c

@@ -1249,6 +1249,7 @@ static int pi433_probe(struct spi_device *spi)
 					     device->minor);
 	if (IS_ERR(device->tx_task_struct)) {
 		dev_dbg(device->dev, "start of send thread failed");
+		retval = PTR_ERR(device->tx_task_struct);
 		goto send_thread_failed;
 	}