iio:potentiostat:lmp91000: Drop of_match_ptr and use generic fw accessors

This change allows use of this driver with ACPI via PRP0001 and removes
an example of an anti pattern I'm trying to remove from IIO.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Matt Ranostay <matt.ranostay@konsulko.com>
Link: https://lore.kernel.org/r/20200910173242.621168-17-jic23@kernel.org

drivers/iio/potentiostat/lmp91000.c

@@ -11,7 +11,7 @@
 #include <linux/module.h>
 #include <linux/i2c.h>
 #include <linux/delay.h>
-#include <linux/of.h>
+#include <linux/mod_devicetable.h>
 #include <linux/regmap.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/buffer.h>
@@ -205,13 +205,12 @@ static const struct iio_info lmp91000_info = {
 static int lmp91000_read_config(struct lmp91000_data *data)
 {
 	struct device *dev = data->dev;
-	struct device_node *np = dev->of_node;
 	unsigned int reg, val;
 	int i, ret;
 
-	ret = of_property_read_u32(np, "ti,tia-gain-ohm", &val);
+	ret = device_property_read_u32(dev, "ti,tia-gain-ohm", &val);
 	if (ret) {
-		if (!of_property_read_bool(np, "ti,external-tia-resistor")) {
+		if (!device_property_read_bool(dev, "ti,external-tia-resistor")) {
 			dev_err(dev, "no ti,tia-gain-ohm defined and external resistor not specified\n");
 			return ret;
 		}
@@ -232,7 +231,7 @@ static int lmp91000_read_config(struct lmp91000_data *data)
 		return ret;
 	}
 
-	ret = of_property_read_u32(np, "ti,rload-ohm", &val);
+	ret = device_property_read_u32(dev, "ti,rload-ohm", &val);
 	if (ret) {
 		val = 100;
 		dev_info(dev, "no ti,rload-ohm defined, default to %d\n", val);
@@ -422,7 +421,7 @@ MODULE_DEVICE_TABLE(i2c, lmp91000_id);
 static struct i2c_driver lmp91000_driver = {
 	.driver = {
 		.name = LMP91000_DRV_NAME,
-		.of_match_table = of_match_ptr(lmp91000_of_match),
+		.of_match_table = lmp91000_of_match,
 	},
 	.probe = lmp91000_probe,
 	.remove = lmp91000_remove,