iio: adc: ti-ads1015: Use correct pga upper bound

The devicetree binding and datasheets (for both the ADS1015 and
ADS1115) show that the PGA index should have a maximum value of 5,
and not 6.
Signed-off-by: Mohammed Billoo <mab.kernel@gmail.com>
Link: https://lore.kernel.org/r/20240106174836.1086714-1-mab.kernel@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ti-ads1015.c

@@ -925,7 +925,7 @@ static int ads1015_client_get_channels_config(struct i2c_client *client)
 
 		if (!fwnode_property_read_u32(node, "ti,gain", &pval)) {
 			pga = pval;
-			if (pga > 6) {
+			if (pga > 5) {
 				dev_err(dev, "invalid gain on %pfw\n", node);
 				fwnode_handle_put(node);
 				return -EINVAL;