regulator: Actually free the regulator in devm_regulator_put()

It turns out that (quite surprisingly) devres_destroy() only undoes the
devres mapping, it doesn't destroy the underlying resource, meaning that
anything using devm_regulator_put() would leak. While we wait for the new
devres_release() which does what we want to get merged open code it in
devm_regulator_put().

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>