mfd: max77620: Fix refcount leak in max77620_initialise_fps

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: 327156c5 ("mfd: max77620: Add core driver for MAX77620/MAX20024")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220601043222.64441-1-linmq006@gmail.com