regulator: rt4831: Add active_discharge_on to fix discharge API

To use set_discharge helper function, active_discharge_on need to be
added.

Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Link: https://lore.kernel.org/r/1648171577-9663-3-git-send-email-u0084500@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>