iio:adc:hi8435: Drop of_match_ptr protection.

Allows use of ACPI with PRP0001 and is generally something we are
trying to avoid having people cut and paste into new drivers without
thinking about it.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
Cc: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>