MIPS: DTS: CI20: fix PMU definitions for ACT8600

There is a ACT8600 on the CI20 board and the bindings of the
ACT8865 driver have changed without updating the CI20 device
tree. Therefore the PMU can not be probed successfully and
is running in power-on reset state.

Fix DT to match the latest act8865-regulator bindings.

Fixes: 73f2b940 ("MIPS: CI20: DTS: Add I2C nodes")
Cc: stable@vger.kernel.org
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Reviewed-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>