ARM: dts: r8a7779: Fix DU reg property

The system uses one address cell and one size cell, not two. Fix the DU
DT node.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>