drm: panel: Fix bpc for OrtusTech COM43H4M85ULC panel

The OrtusTech COM43H4M85ULC panel is a 18-bit RGB panel. Commit
f098f168 ("drm: panel: Fix bus format for OrtusTech COM43H4M85ULC
panel") has fixed the bus formats, but forgot to address the bpc value.
Set it to 6.

Fixes: f098f168 ("drm: panel: Fix bus format for OrtusTech COM43H4M85ULC panel")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200824003254.21904-1-laurent.pinchart@ideasonboard.com

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

@@ -3078,7 +3078,7 @@ static const struct drm_display_mode ortustech_com43h4m85ulc_mode  = {
 static const struct panel_desc ortustech_com43h4m85ulc = {
 	.modes = &ortustech_com43h4m85ulc_mode,
 	.num_modes = 1,
-	.bpc = 8,
+	.bpc = 6,
 	.size = {
 		.width = 56,
 		.height = 93,