Revert "gpiolib: remove set but not used variable 'config'"

This reverts commit e5e42ad2.

This patch came on top of another patch that introduced a regression.
Revert it before addressing the culprit.
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>

drivers/gpio/gpiolib.c

@@ -3047,6 +3047,7 @@ static int gpio_do_set_config(struct gpio_chip *gc, unsigned int offset,
 static int gpio_set_config(struct gpio_chip *gc, unsigned int offset,
 			   enum pin_config_param mode)
 {
+	unsigned long config;
 	unsigned arg;
 
 	switch (mode) {
@@ -3060,6 +3061,7 @@ static int gpio_set_config(struct gpio_chip *gc, unsigned int offset,
 		arg = 0;
 	}
 
+	config = PIN_CONF_PACKED(mode, arg);
 	return gpio_do_set_config(gc, offset, mode);
 }