iio: dac: lpc18xx: Drop dependency on OF

Nothing in this driver depends on OF firmware so drop the dependency
to remove the false impression such a dependency exists.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220413190819.38206-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>