arm64: dts: renesas: r8a774c0: Fix register range of display node

Since the R8A774C0 SoC uses DU{0,1} only, the register block length
should be 0x40000.

Based on commit 06585ed3 ("arm64: dts: renesas: r8a77990: Fix
register range of display node") for R-Car E3.

Fixes: 8ed3a6b2 ("arm64: dts: renesas: r8a774c0: Add display output support")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>