hwrng: meson - Improve error handling for core clock

-ENOENT (ie. "there is no clock") is fine to ignore for an optional
clock, other values are not supposed to be ignored and should be
escalated to the caller (e.g. -EPROBE_DEFER). Ignore -ENOENT by using
devm_clk_get_optional().

While touching this code also add an error message for the fatal errors.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Tested-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/meson-rng.c

@@ -54,9 +54,10 @@ static int meson_rng_probe(struct platform_device *pdev)
 	if (IS_ERR(data->base))
 		return PTR_ERR(data->base);
 
-	data->core_clk = devm_clk_get(dev, "core");
+	data->core_clk = devm_clk_get_optional(dev, "core");
 	if (IS_ERR(data->core_clk))
-		data->core_clk = NULL;
+		return dev_err_probe(dev, PTR_ERR(data->core_clk),
+				     "Failed to get core clock\n");
 
 	if (data->core_clk) {
 		ret = clk_prepare_enable(data->core_clk);