serial: mctrl_gpio: Fix build warnings

Fix the following build warnings:

drivers/tty/serial/serial_mctrl_gpio.c: In function 'mctrl_gpio_init':
drivers/tty/serial/serial_mctrl_gpio.c:110:4: warning: return makes pointer from integer without a cast
    return PTR_ERR(gpios->gpio[i]);
    ^
/home/build/work/batch/drivers/tty/serial/serial_mctrl_gpio.c:90:6: warning: unused variable 'err' [-Wunused-variable]
  int err;
      ^

Return ERR_CAST and remove the unused 'err' variable to fix them.

Fixes: 1d267ea6 ("serial: mctrl-gpio: simplify init routine")
Reported-by: NOlof's autobuilder <build@lixom.net>
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Acked-by: NUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_mctrl_gpio.c

@@ -87,7 +87,6 @@ struct mctrl_gpios *mctrl_gpio_init(struct device *dev, unsigned int idx)
 {
 	struct mctrl_gpios *gpios;
 	enum mctrl_gpio_idx i;
-	int err;
 
 	gpios = devm_kzalloc(dev, sizeof(*gpios), GFP_KERNEL);
 	if (!gpios)
@@ -107,7 +106,7 @@ struct mctrl_gpios *mctrl_gpio_init(struct device *dev, unsigned int idx)
 						      idx, flags);
 
 		if (IS_ERR(gpios->gpio[i]))
-			return PTR_ERR(gpios->gpio[i]);
+			return ERR_CAST(gpios->gpio[i]);
 	}
 
 	return gpios;