drm: panel: simple: Correct bus format for Satoz SAT050AT40H12R2

The Satoz SAT050AT40H12R2 panel is an LVDS panel, the
MEDIA_BUS_FMT_RGB888_1X24 bus format is thus incorrect. Set it to the
correct value MEDIA_BUS_FMT_RGB888_1X7X4_SPWG.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200629233320.8774-3-laurent.pinchart+renesas@ideasonboard.com