iio:potentiostat:lmp91000: change dev_err message

Change dev_err message on line 215 in order to inform that
tia-gain-ohm is not defined and an external resistor is not
specified.
Signed-off-by: Anderson Reis <andersonreisrosa@gmail.com>
Signed-off-by: Lucas Oshiro <lucasseikioshiro@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/potentiostat/lmp91000.c

@@ -212,7 +212,7 @@ static int lmp91000_read_config(struct lmp91000_data *data)
 	ret = of_property_read_u32(np, "ti,tia-gain-ohm", &val);
 	if (ret) {
 		if (!of_property_read_bool(np, "ti,external-tia-resistor")) {
-			dev_err(dev, "no ti,tia-gain-ohm defined");
+			dev_err(dev, "no ti,tia-gain-ohm defined and external resistor not specified\n");
 			return ret;
 		}
 		val = 0;