i2c: pca954x: improve usage of gpiod API

Since 39b2bbe3d715 (gpio: add flags argument to gpiod_get*() functions)
which appeared in v3.17-rc1, the gpiod_get* functions take an additional
parameter that allows to specify direction and initial value for
outputs.

Also there is an *_optional variant that serves well here.  The sematics
is slightly changed here by using it. Now if a reset gpio is specified
and getting hold on it fails, pca954x_probe fails, too.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/muxes/i2c-mux-pca954x.c

@@ -204,9 +204,9 @@ static int pca954x_probe(struct i2c_client *client,
 	i2c_set_clientdata(client, data);
 
 	/* Get the mux out of reset if a reset GPIO is specified. */
-	gpio = devm_gpiod_get(&client->dev, "reset");
-	if (!IS_ERR(gpio))
-		gpiod_direction_output(gpio, 0);
+	gpio = devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_LOW);
+	if (IS_ERR(gpio))
+		return PTR_ERR(gpio);
 
 	/* Write the mux register at addr to verify
 	 * that the mux is in fact present. This also