gpiolib: Use proper type for bias enumerator in gpio_set_bias()

First of all, bias has a special type as being a part of enum pin_config_param.
Second, 0 is also defined bias which is equivalent to BUS_HOLD.

Taking into account above, change type of bias variable and refactor
gpio_set_bias() in a way that it doesn't use BUS_HOLD as a place holder.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20201009184359.16427-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -2256,21 +2256,22 @@ static int gpio_set_config(struct gpio_desc *desc, enum pin_config_param mode)
 
 static int gpio_set_bias(struct gpio_desc *desc)
 {
-	int bias = 0;
-	int ret = 0;
+	enum pin_config_param bias;
+	int ret;
 
 	if (test_bit(FLAG_BIAS_DISABLE, &desc->flags))
 		bias = PIN_CONFIG_BIAS_DISABLE;
 	else if (test_bit(FLAG_PULL_UP, &desc->flags))
 		bias = PIN_CONFIG_BIAS_PULL_UP;
 	else if (test_bit(FLAG_PULL_DOWN, &desc->flags))
 		bias = PIN_CONFIG_BIAS_PULL_DOWN;
+	else
+		return 0;
+
+	ret = gpio_set_config(desc, bias);
+	if (ret != -ENOTSUPP)
+		return ret;
 
-	if (bias) {
-		ret = gpio_set_config(desc, bias);
-		if (ret != -ENOTSUPP)
-			return ret;
-	}
 	return 0;
 }