clocksource: Put nodes passed to CLOCKSOURCE_OF_DECLARE callbacks centrally

Instead of letting each driver call of_node_put do it centrally in the
loop that also calls the CLOCKSOURCE_OF_DECLARE callbacks. This is less
prone to error and also moves getting and putting the references into the
same function.

Consequently all respective of_node_put calls in drivers are removed.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: David Brown <davidb@codeaurora.org>