ASoC: Intel: bytcht_es8316: Switch to use gpiod_get_optional()

First of all, replace indexed API by plain one since we have index 0.
Second, switch to optional variant and drop duplicated code.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20211006150428.16434-3-andriy.shevchenko@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/intel/boards/bytcht_es8316.c

@@ -566,16 +566,12 @@ static int snd_byt_cht_es8316_mc_probe(struct platform_device *pdev)
 
 	devm_acpi_dev_add_driver_gpios(codec_dev, byt_cht_es8316_gpios);
 	priv->speaker_en_gpio =
-		gpiod_get_index(codec_dev, "speaker-enable", 0,
-				/* see comment in byt_cht_es8316_resume */
-				GPIOD_OUT_LOW | GPIOD_FLAGS_BIT_NONEXCLUSIVE);
-
+		gpiod_get_optional(codec_dev, "speaker-enable",
+				   /* see comment in byt_cht_es8316_resume() */
+				   GPIOD_OUT_LOW | GPIOD_FLAGS_BIT_NONEXCLUSIVE);
 	if (IS_ERR(priv->speaker_en_gpio)) {
 		ret = PTR_ERR(priv->speaker_en_gpio);
 		switch (ret) {
-		case -ENOENT:
-			priv->speaker_en_gpio = NULL;
-			break;
 		default:
 			dev_err(dev, "get speaker GPIO failed: %d\n", ret);
 			fallthrough;