iio: kxsd9: Don't return error code in trigger handler

IIO trigger handlers need to return one of the irqreturn_t values.
Returning an error code is not supported.

The kxsd9 interrupt handler returns an error code if reading the data
registers fails. In addition when exiting due to an error the trigger
handler does not call `iio_trigger_notify_done()`. Which when not done
keeps the triggered disabled forever.

Modify the code so that the function returns a valid irqreturn_t value as
well as calling `iio_trigger_notify_done()` on all exit paths.

Since we can't return the error code make sure to at least log it as part
of the error message.

Fixes: 0427a106a98a ("iio: accel: kxsd9: Add triggered buffer handling")
Signed-off-by: Lars-Peter Clausen <[e-mail]>
Reviewed-by: Linus Walleij <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Cc: <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/accel/kxsd9.c

···
 			       hw_values.chan,
 			       sizeof(hw_values.chan));
 	if (ret) {
-		dev_err(st->dev,
-			"error reading data\n");
-		return ret;
+		dev_err(st->dev, "error reading data: %d\n", ret);
+		goto out;
 	}
 
 	iio_push_to_buffers_with_timestamp(indio_dev,
 					   &hw_values,
 					   iio_get_time_ns(indio_dev));
+out:
 	iio_trigger_notify_done(indio_dev->trig);
 
 	return IRQ_HANDLED;