iio:adc:ti-adc161s626: Drop of_match_ptr protection.

iio:adc:ti-adc161s626: Drop of_match_ptr protection.

Dropping this allows use of ACPI PRP0001.

I'm also looking to drop all of_match_ptr use in IIO in order to avoid
it getting cut and paste into new drivers in the future.

Also add a direct include of mod_devicetable.h to reflect the use
of struct of_device_id.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Matt Ranostay <matt.ranostay@konsulko.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>