class_create if succeeded returns a pointer to the struct class,
and if it fails, it returns a value enclosed by the pointer, which
can be read by using PTR_ERR.
Handle the error and return it.
result is for error checking of the alloc_chrdev_region, instead
ret can be used, and also if the alloc_chrdev_region fail,
we are still returning -ENODEV, use ret and the error path will
take care of returning of the ret.