drm: renesas: rcar-du: use proper naming for R-Car

Not RCAR, but R-Car.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/20250522103530.51972-2-wsa+renesas@sang-engineering.com


Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>