iio: adc: at91-sama5d2_adc: move the check of oversampling in its function

Oversampling values are checked anyway in at91_adc_emr_config(). Remove
the checking of these from at91_adc_write_raw() and return -EINVAL
instead in at91_adc_emr_config().
Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220803102855.2191070-8-claudiu.beznea@microchip.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/at91-sama5d2_adc.c

@@ -728,8 +728,8 @@ static void at91_adc_eoc_ena(struct at91_adc_state *st, unsigned int channel)
 		at91_adc_writel(st, EOC_IER, BIT(channel));
 }
 
-static void at91_adc_config_emr(struct at91_adc_state *st,
-				u32 oversampling_ratio)
+static int at91_adc_config_emr(struct at91_adc_state *st,
+			       u32 oversampling_ratio)
 {
 	/* configure the extended mode register */
 	unsigned int emr = at91_adc_readl(st, EMR);
@@ -755,9 +755,13 @@ static void at91_adc_config_emr(struct at91_adc_state *st,
 		emr |= AT91_SAMA5D2_EMR_OSR(AT91_SAMA5D2_EMR_OSR_16SAMPLES,
 					    osr_mask);
 		break;
+	default:
+		return -EINVAL;
 	}
 
 	at91_adc_writel(st, EMR, emr);
+
+	return 0;
 }
 
 static int at91_adc_adjust_val_osr(struct at91_adc_state *st, int *val)
@@ -1650,9 +1654,6 @@ static int at91_adc_write_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
-		if ((val != AT91_OSR_1SAMPLES) && (val != AT91_OSR_4SAMPLES) &&
-		    (val != AT91_OSR_16SAMPLES))
-			return -EINVAL;
 		/* if no change, optimize out */
 		if (val == st->oversampling_ratio)
 			return 0;
@@ -1661,12 +1662,13 @@ static int at91_adc_write_raw(struct iio_dev *indio_dev,
 		if (ret)
 			return ret;
 		mutex_lock(&st->lock);
-		st->oversampling_ratio = val;
 		/* update ratio */
-		at91_adc_config_emr(st, val);
+		ret = at91_adc_config_emr(st, val);
+		if (!ret)
+			st->oversampling_ratio = val;
 		mutex_unlock(&st->lock);
 		iio_device_release_direct_mode(indio_dev);
-		return 0;
+		return ret;
 	case IIO_CHAN_INFO_SAMP_FREQ:
 		if (val < st->soc_info.min_sample_rate ||
 		    val > st->soc_info.max_sample_rate)