iio:potentiometer:max5432: Drop of_match_ptr and use generic fw accessors

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 headers to reflect this change.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20200910173242.621168-4-jic23@kernel.org

drivers/iio/potentiometer/max5432.c

@@ -11,8 +11,8 @@
 #include <linux/iio/iio.h>
 #include <linux/limits.h>
 #include <linux/module.h>
-#include <linux/of.h>
-#include <linux/of_device.h>
+#include <linux/mod_devicetable.h>
+#include <linux/property.h>
 
 /* All chip variants have 32 wiper positions. */
 #define MAX5432_MAX_POS 31
@@ -100,7 +100,7 @@ static int max5432_probe(struct i2c_client *client,
 
 	data = iio_priv(indio_dev);
 	data->client = client;
-	data->ohm = (unsigned long)of_device_get_match_data(dev);
+	data->ohm = (unsigned long)device_get_match_data(dev);
 
 	indio_dev->info = &max5432_info;
 	indio_dev->channels = max5432_channels;
@@ -122,7 +122,7 @@ MODULE_DEVICE_TABLE(of, max5432_dt_ids);
 static struct i2c_driver max5432_driver = {
 	.driver = {
 		.name = "max5432",
-		.of_match_table = of_match_ptr(max5432_dt_ids),
+		.of_match_table = max5432_dt_ids,
 	},
 	.probe = max5432_probe,
 };