iio: adc: stm32-dfsdm: fix clock source selection

Add missing clock source selection. In case "audio" clock is provided,
it's unused currently: "dfsdm" clock is wrongly used by default.

Fixes: bed73904 ("IIO: ADC: add stm32 DFSDM core support")
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Acked-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/stm32-dfsdm-core.c

@@ -83,7 +83,7 @@ int stm32_dfsdm_start_dfsdm(struct stm32_dfsdm *dfsdm)
 {
 	struct dfsdm_priv *priv = container_of(dfsdm, struct dfsdm_priv, dfsdm);
 	struct device *dev = &priv->pdev->dev;
-	unsigned int clk_div = priv->spi_clk_out_div;
+	unsigned int clk_div = priv->spi_clk_out_div, clk_src;
 	int ret;
 
 	if (atomic_inc_return(&priv->n_active_ch) == 1) {
@@ -100,6 +100,14 @@ int stm32_dfsdm_start_dfsdm(struct stm32_dfsdm *dfsdm)
 			}
 		}
 
+		/* select clock source, e.g. 0 for "dfsdm" or 1 for "audio" */
+		clk_src = priv->aclk ? 1 : 0;
+		ret = regmap_update_bits(dfsdm->regmap, DFSDM_CHCFGR1(0),
+					 DFSDM_CHCFGR1_CKOUTSRC_MASK,
+					 DFSDM_CHCFGR1_CKOUTSRC(clk_src));
+		if (ret < 0)
+			goto disable_aclk;
+
 		/* Output the SPI CLKOUT (if clk_div == 0 clock if OFF) */
 		ret = regmap_update_bits(dfsdm->regmap, DFSDM_CHCFGR1(0),
 					 DFSDM_CHCFGR1_CKOUTDIV_MASK,