drm/panel: simple: Fix the bus format for the Ontat panel

This fixes bad color output.  When I was first testing the device I
had the DPI hardware set to 666 mode, but apparently in the refactor
to use the bus_format information from the panel driver, I failed to
actually update the panel.
Signed-off-by: Eric Anholt <eric@anholt.net>
Fixes: e8b6f561 ("drm/panel: simple: Add the 7" DPI panel from Adafruit")
Cc: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180309233332.1769-1-eric@anholt.net

drivers/gpu/drm/panel/panel-simple.c

@@ -1597,7 +1597,7 @@ static const struct panel_desc ontat_yx700wv03 = {
 		.width = 154,
 		.height = 83,
 	},
-	.bus_format = MEDIA_BUS_FMT_RGB888_1X24,
+	.bus_format = MEDIA_BUS_FMT_RGB666_1X18,
 };
 
 static const struct drm_display_mode ortustech_com43h4m85ulc_mode  = {