iio: adc: aspeed: Fix refcount leak in aspeed_adc_set_trim_data

iio: adc: aspeed: Fix refcount leak in aspeed_adc_set_trim_data

of_find_node_by_name() returns a node pointer with refcount
incremented, we should use of_node_put() on it when done.
Add missing of_node_put() to avoid refcount leak.

Fixes: d0a4c17b4073 ("iio: adc: aspeed: Get and set trimming data.")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Link: https://lore.kernel.org/r/20220516075206.34580-1-linmq006@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>