iio: adc: aspeed: Fix refcount leak in aspeed_adc_set_trim_data

In the Linux kernel, the following vulnerability has been resolved: 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.