regulator: core: Add helper to put of_nodes from matches

As of_regulator_match will take an of_node reference to each matched
regulator, it makes sense to provide a helper to put all those
references. This patch does that.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@linaro.org>