iio:adc:lpc32xx: Drop of_match_ptr protection

Whilst is unlikely anyone will be using this part with an ACPI PRP0001
based binding any time soon, we are getting a lot of cut and pasting
of this pattern so I am looking to remove it entirely from IIO.

In this case CONFIG_OF protections also removed and
mod_devicetable.h include added given direct use of struct of_device_id.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>