pwm: meson: Use devm_clk_get_optional() to get the input clock

Simplify the code which fetches the input clock for a PWM channel by
using devm_clk_get_optional().
This comes with a small functional change: previously all errors except
EPROBE_DEFER were ignored. Now all other errors are also treated as
errors. If no input clock is present devm_clk_get_optional() will return
NULL instead of an error which matches the behavior of the old code.

Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-meson.c

@@ -483,14 +483,9 @@ static int meson_pwm_init_channels(struct meson_pwm *meson,
 
 		snprintf(name, sizeof(name), "clkin%u", i);
 
-		channel->clk_parent = devm_clk_get(dev, name);
-		if (IS_ERR(channel->clk_parent)) {
-			err = PTR_ERR(channel->clk_parent);
-			if (err == -EPROBE_DEFER)
-				return err;
-
-			channel->clk_parent = NULL;
-		}
+		channel->clk_parent = devm_clk_get_optional(dev, name);
+		if (IS_ERR(channel->clk_parent))
+			return PTR_ERR(channel->clk_parent);
 	}
 
 	return 0;