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

commit 65f20301 upstream.

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: 0e589d5f ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>