iio: adc: stm32-adc: fix channel sampling time init

Fix channel init for ADC generic channel bindings.
In generic channel initialization, stm32_adc_smpr_init() is called to
initialize channel sampling time. The "st,min-sample-time-ns" property
is an optional property. If it is not defined, stm32_adc_smpr_init() is
currently skipped.
However stm32_adc_smpr_init() must always be called, to force a minimum
sampling time for the internal channels, as the minimum sampling time is
known. Make stm32_adc_smpr_init() call unconditional.

Fixes: 796e5d0b1e ("iio: adc: stm32-adc: use generic binding for sample-time")
Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20221012142205.13041-2-olivier.moysan@foss.st.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/stm32-adc.c

@@ -2086,18 +2086,19 @@ static int stm32_adc_generic_chan_init(struct iio_dev *indio_dev,
 		stm32_adc_chan_init_one(indio_dev, &channels[scan_index], val,
 					vin[1], scan_index, differential);
 
+		val = 0;
 		ret = fwnode_property_read_u32(child, "st,min-sample-time-ns", &val);
 		/* st,min-sample-time-ns is optional */
-		if (!ret) {
-			stm32_adc_smpr_init(adc, channels[scan_index].channel, val);
-			if (differential)
-				stm32_adc_smpr_init(adc, vin[1], val);
-		} else if (ret != -EINVAL) {
+		if (ret && ret != -EINVAL) {
 			dev_err(&indio_dev->dev, "Invalid st,min-sample-time-ns property %d\n",
 				ret);
 			goto err;
 		}
 
+		stm32_adc_smpr_init(adc, channels[scan_index].channel, val);
+		if (differential)
+			stm32_adc_smpr_init(adc, vin[1], val);
+
 		scan_index++;
 	}