regulator: rk808: Fix memory leak

The memory allocated in rk808_regulator_probe() needs to be freed when the
module is unloaded. Thus pass &pdev->dev rather than &client->dev to
devm_kzalloc.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@linaro.org>