iio: adc: adi-axi-adc: support modified prbs23

Add support for configuring the prbs23 sequence.
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240802-dev-iio-backend-add-debugfs-v2-4-4cb62852f0d0@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/adi-axi-adc.c

@@ -199,6 +199,10 @@ static int axi_adc_test_pattern_set(struct iio_backend *back,
 		return regmap_update_bits(st->regmap, ADI_AXI_ADC_REG_CHAN_CTRL_3(chan),
 					  ADI_AXI_ADC_CHAN_PN_SEL_MASK,
 					  FIELD_PREP(ADI_AXI_ADC_CHAN_PN_SEL_MASK, 0));
+	case IIO_BACKEND_ADI_PRBS_23A:
+		return regmap_update_bits(st->regmap, ADI_AXI_ADC_REG_CHAN_CTRL_3(chan),
+					  ADI_AXI_ADC_CHAN_PN_SEL_MASK,
+					  FIELD_PREP(ADI_AXI_ADC_CHAN_PN_SEL_MASK, 1));
 	default:
 		return -EINVAL;
 	}