power: supply: Fix refcount leak in rk817_charger_probe

of_get_child_by_name() 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: 11cb8da0 ("power: supply: Add charger driver for Rockchip RK817")
Signed-off-by: Qiheng Lin <linqiheng@huawei.com>
Reviewed-by: Chris Morgan <macromorgan@hotmail.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>