arm64: dts: renesas: r8a77990: Fix register range of display node

Since the R8A77990 SoC uses DU{0,1}, the range from the base address to
the 0x4000 address is used.
This patch fixed it.

Fixes: 13ee2bfc ("arm64: dts: renesas: r8a77990: Add display output support")
Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
Signed-off-by: Yoshihiro Kaneko <ykaneko0929@gmail.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>