hwmon: (cgbc-hwmon) Add missing NULL check after devm_kzalloc()

In the Linux kernel, the following vulnerability has been resolved: hwmon: (cgbc-hwmon) Add missing NULL check after devm_kzalloc() The driver allocates memory for sensor data using devm_kzalloc(), but did not check if the allocation succeeded. In case of memory allocation failure, dereferencing the NULL pointer would lead to a kernel crash. Add a NULL pointer check and return -ENOMEM to handle allocation failure properly.