drm/panel: simple: Fix innolux_g121i1_l01 bus_format

innolux_g121i1_l01 sets bpc to 6, so use the corresponding bus format:
MEDIA_BUS_FMT_RGB666_1X7X3_SPWG.

Fixes: 4ae13e48

 ("drm/panel: simple: Add more properties to Innolux G121I1-L01")
Signed-off-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220826165021.1592532-1-festevam@denx.de