iio:potentiometer:ds1803: Drop of_match_ptr and CONFIG_OF protections

These prevent use of this driver with ACPI via PRP0001 and are
an example of an anti pattern I'm trying to remove from IIO.
Drop them to remove this restriction.

Also switch of.h for mod_devicetable.h include given use of
struct of_device_id which is defined in that header.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Slawomir Stepien <sst@poczta.fm>
Link: https://lore.kernel.org/r/20200910173242.621168-3-jic23@kernel.org

drivers/iio/potentiometer/ds1803.c

@@ -14,7 +14,7 @@
 #include <linux/i2c.h>
 #include <linux/iio/iio.h>
 #include <linux/module.h>
-#include <linux/of.h>
+#include <linux/mod_devicetable.h>
 
 #define DS1803_MAX_POS		255
 #define DS1803_WRITE(chan)	(0xa8 | ((chan) + 1))
@@ -134,7 +134,6 @@ static int ds1803_probe(struct i2c_client *client,
 	return devm_iio_device_register(dev, indio_dev);
 }
 
-#if defined(CONFIG_OF)
 static const struct of_device_id ds1803_dt_ids[] = {
 	{ .compatible = "maxim,ds1803-010", .data = &ds1803_cfg[DS1803_010] },
 	{ .compatible = "maxim,ds1803-050", .data = &ds1803_cfg[DS1803_050] },
@@ -142,7 +141,6 @@ static const struct of_device_id ds1803_dt_ids[] = {
 	{}
 };
 MODULE_DEVICE_TABLE(of, ds1803_dt_ids);
-#endif /* CONFIG_OF */
 
 static const struct i2c_device_id ds1803_id[] = {
 	{ "ds1803-010", DS1803_010 },
@@ -155,7 +153,7 @@ MODULE_DEVICE_TABLE(i2c, ds1803_id);
 static struct i2c_driver ds1803_driver = {
 	.driver = {
 		.name	= "ds1803",
-		.of_match_table = of_match_ptr(ds1803_dt_ids),
+		.of_match_table = ds1803_dt_ids,
 	},
 	.probe		= ds1803_probe,
 	.id_table	= ds1803_id,