power: supply: ab8500: Fix error handling when calling iio_read_channel_processed()

The ab8500_charger_get_[ac|vbus]_[current|voltage]() functions should
return an error code on error.

Up to now, an un-initialized value is returned.
This makes the error handling of the callers un-reliable.

Return the error code instead, to fix the issue.

Fixes: 97ab78bac5d0 ("power: supply: ab8500_charger: Convert to IIO ADC")
Signed-off-by: Christophe JAILLET <[e-mail]>
Reviewed-by: Jonathan Cameron <[e-mail]>
Reviewed-by: Linus Walleij <[e-mail]>
Link: https://lore.kernel.org/r/f9f6564233[e-mail]
Signed-off-by: Sebastian Reichel <[e-mail]>

drivers/power/supply/ab8500_charger.c

···
 	/* Only measure voltage if the charger is connected */
 	if (di->ac.charger_connected) {
 		ret = iio_read_channel_processed(di->adc_main_charger_v, &vch);
-		if (ret < 0)
+		if (ret < 0) {
 			dev_err(di->dev, "%s ADC conv failed,\n", __func__);
+			return ret;
+		}
 	} else {
 		vch = 0;
 	}
···
 	/* Only measure voltage if the charger is connected */
 	if (di->usb.charger_connected) {
 		ret = iio_read_channel_processed(di->adc_vbus_v, &vch);
-		if (ret < 0)
+		if (ret < 0) {
 			dev_err(di->dev, "%s ADC conv failed,\n", __func__);
+			return ret;
+		}
 	} else {
 		vch = 0;
 	}
···
 	/* Only measure current if the charger is online */
 	if (di->usb.charger_online) {
 		ret = iio_read_channel_processed(di->adc_usb_charger_c, &ich);
-		if (ret < 0)
+		if (ret < 0) {
 			dev_err(di->dev, "%s ADC conv failed,\n", __func__);
+			return ret;
+		}
 	} else {
 		ich = 0;
 	}
···
 	/* Only measure current if the charger is online */
 	if (di->ac.charger_online) {
 		ret = iio_read_channel_processed(di->adc_main_charger_c, &ich);
-		if (ret < 0)
+		if (ret < 0) {
 			dev_err(di->dev, "%s ADC conv failed,\n", __func__);
+			return ret;
+		}
 	} else {
 		ich = 0;
 	}