ASoC: simple-amplifier: Make gpio property optional

Some amplifier may not have a GPIO to control the power, but instead simply
rely on the regulator to power up and down the amplifier.

In order to support those setups, let's make the GPIO optional.
Signed-off-by: Mylène Josserand <mylene.josserand@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/simple-amplifier.txt

@@ -2,9 +2,9 @@ Simple Amplifier Audio Driver
 
 Required properties:
 - compatible : "dioo,dio2125" or "simple-audio-amplifier"
-- enable-gpios : the gpio connected to the enable pin of the simple amplifier
 
 Optional properties:
+- enable-gpios : the gpio connected to the enable pin of the simple amplifier
 - VCC-supply   : power supply for the device, as covered
                  in Documentation/devicetree/bindings/regulator/regulator.txt
 

sound/soc/codecs/simple-amplifier.c

@@ -89,7 +89,8 @@ static int simple_amp_probe(struct platform_device *pdev)
 		return -ENOMEM;
 	platform_set_drvdata(pdev, priv);
 
-	priv->gpiod_enable = devm_gpiod_get(dev, "enable", GPIOD_OUT_LOW);
+	priv->gpiod_enable = devm_gpiod_get_optional(dev, "enable",
+						     GPIOD_OUT_LOW);
 	if (IS_ERR(priv->gpiod_enable)) {
 		err = PTR_ERR(priv->gpiod_enable);
 		if (err != -EPROBE_DEFER)