ARM: Cygnus: dts: fix NAND nodes names

[ Upstream commit e256b48a3b07ee1ae4bfa60abbf509ba8e386862 ]

This matches nand-controller.yaml requirements.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>