rtc: gamecube: Fix refcount leak in gamecube_rtc_read_offset_from_sram

The of_find_compatible_node() function returns a node pointer with
refcount incremented, We should use of_node_put() on it when done
Add the missing of_node_put() to release the refcount.

Fixes: 86559400

 ("rtc: gamecube: Add a RTC driver for the GameCube, Wii and Wii U")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220309092225.6930-1-linmq006@gmail.com