iio: ssp: use PLATFORM_DEVID_NONE

Use PLATFORM_DEVID_NONE define instead of "-1" value because:
 - it brings some meaning,
 - it might point attention why auto device ID was not used.
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200921204939.20341-1-krzk@kernel.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/common/ssp_sensors/ssp_dev.c

@@ -503,7 +503,8 @@ static int ssp_probe(struct spi_device *spi)
 		return -ENODEV;
 	}
 
-	ret = mfd_add_devices(&spi->dev, -1, sensorhub_sensor_devs,
+	ret = mfd_add_devices(&spi->dev, PLATFORM_DEVID_NONE,
+			      sensorhub_sensor_devs,
 			      ARRAY_SIZE(sensorhub_sensor_devs), NULL, 0, NULL);
 	if (ret < 0) {
 		dev_err(&spi->dev, "mfd add devices fail\n");