hwmon: (axi-fan-control) Fix possible NULL pointer dereference

In the Linux kernel, the following vulnerability has been resolved: hwmon: (axi-fan-control) Fix possible NULL pointer dereference axi_fan_control_irq_handler(), dependent on the private axi_fan_control_data structure, might be called before the hwmon device is registered. That will cause an "Unable to handle kernel NULL pointer dereference" error.