gpiolib: Introduce GPIO_LOOKUP_FLAGS_DEFAULT

Since GPIO library operates with enumerator when it's subject to handle
the GPIO lookup flags, it will be better to clearly see what default means.

Thus, introduce GPIO_LOOKUP_FLAGS_DEFAULT entry to describe
the default assumptions.

While here, replace 0 by newly introduced constant.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
index c5547df..aec7bd8 100644
--- a/drivers/gpio/gpiolib-of.c
+++ b/drivers/gpio/gpiolib-of.c
@@ -386,7 +386,7 @@ static struct gpio_desc *of_parse_own_gpio(struct device_node *np,
 		return ERR_PTR(-EINVAL);
 
 	xlate_flags = 0;
-	*lflags = 0;
+	*lflags = GPIO_LOOKUP_FLAGS_DEFAULT;
 	*dflags = 0;
 
 	ret = of_property_read_u32(chip_np, "#gpio-cells", &tmp);