w1: fix NULL pointer dereference in probe

The w1_uart_probe() function calls w1_uart_serdev_open() (which includes
devm_serdev_device_open()) before setting the client ops via
serdev_device_set_client_ops(). This ordering can trigger a NULL pointer
dereference in the serdev controller's receive_buf handler, as it assumes
serdev->ops is valid when SERPORT_ACTIVE is set.

This is similar to the issue fixed in commit 5e700b384ec1
("platform/chrome: cros_ec_uart: properly fix race condition") where
devm_serdev_device_open() was called before fully initializing the
device.

Fix the race by ensuring client ops are set before enabling the port via
w1_uart_serdev_open().

Fixes: a3c08804364e ("w1: add UART w1 bus driver")
Signed-off-by: Chenyuan Yang <[e-mail]>
Acked-by: Christoph Winklhofer <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Krzysztof Kozlowski <[e-mail]>

drivers/w1/masters/w1-uart.c

···
 	init_completion(&w1dev->rx_byte_received);
 	mutex_init(&w1dev->rx_mutex);
 
+	serdev_device_set_drvdata(serdev, w1dev);
+	serdev_device_set_client_ops(serdev, &w1_uart_serdev_ops);
 	ret = w1_uart_serdev_open(w1dev);
 	if (ret < 0)
 		return ret;
-	serdev_device_set_drvdata(serdev, w1dev);
-	serdev_device_set_client_ops(serdev, &w1_uart_serdev_ops);
 
 	return w1_add_master_device(&w1dev->bus);
 }