sample: drivers: adc: Honnor CONFIG_ADC_CONFIGURABLE_INPUTS

Some adc drivers, like adc_sam0, doesn't look at channel_id
when setting up the adc channel, but rely on the input_positive
and input_negative members.

With this change the sample project also supports e.g.
samd21 based boards using other pins than AIN[0].

This is exemplified by adding arduino_zero overlay using AIN[10]

Signed-off-by: Kim Bøndergaard <[email protected]>

Author: KimBP

samples/drivers/adc/boards/arduino_zero.overlay

@@ -0,0 +1,16 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Copyright (c) 2022 Kim Bøndergaard <[email protected]>
+ */
+
+/ {
+	zephyr,user {
+		/* J106.6 (A5) aka D21G18, pin PB02_AIN10 */
+		io-channels = <&adc 10>;
+	};
+};
+
+&adc {
+	status = "okay";
+};

samples/drivers/adc/src/main.c

@@ -49,7 +49,11 @@ struct adc_channel_cfg channel_cfg = {
 	.acquisition_time = ADC_ACQUISITION_TIME,
 	/* channel ID will be overwritten below */
 	.channel_id = 0,
-	.differential = 0
+	.differential = 0,
+#ifdef CONFIG_ADC_CONFIGURABLE_INPUTS
+	.input_negative = 0,
+	.input_positive = 0,
+#endif
 };
 
 struct adc_sequence sequence = {
@@ -80,6 +84,9 @@ void main(void)
 		channel_cfg.input_positive = SAADC_CH_PSELP_PSELP_AnalogInput0
 					     + channel_ids[i];
 #endif
+#ifdef CONFIG_ADC_CONFIGURABLE_INPUTS
+		channel_cfg.input_positive = channel_ids[i];
+#endif
 
 		adc_channel_setup(dev_adc, &channel_cfg);