arm64: dts: rockchip: fix LDO_REG4 / LDO_REG7 confusion on rk3368-lion

LDO_REG7 is used for generating VCC_18.
LDO_REG4 is not connected to anything - delete it.

Signed-off-by: Jakob Unterwurzacher <jakob.unterwurzacher@theobroma-systems.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20210922230429.2162535-1-heiko@sntech.de