drm: rcar-du: Use the correct naming for ODPM fields in DEFR6

drm: rcar-du: Use the correct naming for ODPM fields in DEFR6

The naming of the fields for the ODPM signals in the DU extensional
function control register 6 (DEFR6) is incorrect against the data sheets
for both R-Car Gen2 and R-Car Gen3.

Rename the fields to match the datasheet.

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>