MIPS: DTS: CI20: fix how ddc power is enabled

Originally we proposed a new hdmi-5v-supply regulator reference
for CI20 device tree but that was superseded by a better idea to use
the already defined "ddc-en-gpios" property of the "hdmi-connector".

Since "MIPS: DTS: CI20: Add DT nodes for HDMI setup" has already
been applied to v5.17-rc1, we add this on top.

Fixes: ae1b8d2c

 ("MIPS: DTS: CI20: Add DT nodes for HDMI setup")
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>