ASoC: stm32: sai: 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/f7987f18dadf77bfa09969fd4c82d5a0f4e4e3b7.1684594838.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/stm/stm32_sai_sub.c

@@ -1485,12 +1485,9 @@ static int stm32_sai_sub_parse_of(struct platform_device *pdev,
 		if (ret < 0)
 			return ret;
 	} else {
-		sai->sai_mclk = devm_clk_get(&pdev->dev, "MCLK");
-		if (IS_ERR(sai->sai_mclk)) {
-			if (PTR_ERR(sai->sai_mclk) != -ENOENT)
+		sai->sai_mclk = devm_clk_get_optional(&pdev->dev, "MCLK");
+		if (IS_ERR(sai->sai_mclk))
 			return PTR_ERR(sai->sai_mclk);
-			sai->sai_mclk = NULL;
-		}
 	}
 
 	return 0;