regulator: da9121: Prevent current limit change when enabled

Prevent changing current limit when enabled as a precaution against
possibile instability due to tight integration with switching cycle

Signed-off-by: Adam Ward <Adam.Ward.opensource@diasemi.com>
Link: https://lore.kernel.org/r/52ee682476004a1736c1e0293358987319c1c415.1638223185.git.Adam.Ward.opensource@diasemi.com


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