w1: fix NULL pointer dereference in probe

In the Linux kernel, the following vulnerability has been resolved: 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().