iio: adc: adi-axi-adc: Fix refcount leak in adi_axi_adc_attach_client

of_parse_phandle() returns a node pointer with refcount
incremented, we should use of_node_put() on it when not need anymore.
Add missing of_node_put() to avoid refcount leak.

Fixes: ef040706

 ("iio: adc: adi-axi-adc: add support for AXI ADC IP core")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Link: https://lore.kernel.org/r/20220524074517.45268-1-linmq006@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>