adc: meson-saradc: fix regmap_init_mem call

The SARADC driver was merged after the following commit :
commit d35812368a59 ("regmap: change regmap_init_mem() to take ofnode instead udevice")
Thus breaking build, this patch fixes the regmap_init_mem accordingly.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/drivers/adc/meson-saradc.c b/drivers/adc/meson-saradc.c
index bcab76d..f7c919d 100644
--- a/drivers/adc/meson-saradc.c
+++ b/drivers/adc/meson-saradc.c
@@ -654,7 +654,7 @@
 	struct meson_saradc_priv *priv = dev_get_priv(dev);
 	int ret;
 
-	ret = regmap_init_mem(dev, &priv->regmap);
+	ret = regmap_init_mem(dev_ofnode(dev), &priv->regmap);
 	if (ret)
 		return ret;