arm: dts: renesas: r8a77980: Remove r8a77970 DU compatible

arm: dts: renesas: r8a77980: Remove r8a77970 DU compatible

The r8a77970 was added with a compatible string for a different device
rather than adding the correct compatible to the driver.

Remove the unnecessary compatible which is for a different platform.

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Link: https://lore.kernel.org/r/20190912103734.1879-1-kieran.bingham+renesas@ideasonboard.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>