ASoC: adau1761: Use the devm_clk_get_optional() helper

Use devm_clk_get_optional() instead of hand writing it.
This saves some LoC and improves the semantic.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/ab0fe7e7ecf965df84b9516ba65428af9b3805c1.1684594081.git.christophe.jaillet@wanadoo.frSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/adau17x1.c

@@ -1059,13 +1059,12 @@ int adau17x1_probe(struct device *dev, struct regmap *regmap,
 	if (!adau)
 		return -ENOMEM;
 
-	adau->mclk = devm_clk_get(dev, "mclk");
-	if (IS_ERR(adau->mclk)) {
-		if (PTR_ERR(adau->mclk) != -ENOENT)
-			return PTR_ERR(adau->mclk);
-		/* Clock is optional (for the driver) */
-		adau->mclk = NULL;
-	} else if (adau->mclk) {
+	/* Clock is optional (for the driver) */
+	adau->mclk = devm_clk_get_optional(dev, "mclk");
+	if (IS_ERR(adau->mclk))
+		return PTR_ERR(adau->mclk);
+
+	if (adau->mclk) {
 		adau->clk_src = ADAU17X1_CLK_SRC_PLL_AUTO;
 
 		/*