iio: adc: at91_adc: fix possible memory leak in at91_adc_allocate_trigger()

If iio_trigger_register() returns error, it should call iio_trigger_free()
to give up the reference that hold in iio_trigger_alloc(), so that it can
call iio_trig_release() to free memory when the refcount hit to 0.

Fixes: 0e589d5 ("ARM: AT91: IIO: Add AT91 ADC driver.")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20221024084511.815096-1-yangyingliang@huawei.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: Yang Yingliang

drivers/iio/adc/at91_adc.c

@@ -634,8 +634,10 @@ static struct iio_trigger *at91_adc_allocate_trigger(struct iio_dev *idev,
 	trig->ops = &at91_adc_trigger_ops;
 
 	ret = iio_trigger_register(trig);
-	if (ret)
+	if (ret) {
+		iio_trigger_free(trig);
 		return NULL;
+	}
 
 	return trig;
 }