memory: of: Fix refcount leak bug in of_get_ddr_timings()

We should add the of_node_put() when breaking out of
for_each_child_of_node() as it will automatically increase
and decrease the refcount.

Fixes: e6b42eb6 ("memory: emif: add device tree support to emif driver")
Signed-off-by: Liang He <windhl@126.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220719085640.1210583-1-windhl@126.com