gpu: ipu-v3: ipu-dc: don't bug out on invalid bus_format

If imx-drm is combined with a bridge or panel that requests an
unsupported format, warn and use a default mapping instead of
hanging the machine. The worst that can happen here are wrong
colors.

Signed-off-by: Philipp Zabel <[e-mail]>

drivers/gpu/ipu-v3/ipu-dc.c

···
 static int ipu_bus_format_to_map(u32 fmt)
 {
 	switch (fmt) {
+	default:
+		WARN_ON(1);
+		/* fall-through */
 	case MEDIA_BUS_FMT_RGB888_1X24:
 		return IPU_DC_MAP_RGB24;
 	case MEDIA_BUS_FMT_RGB565_1X16:
···
 		return IPU_DC_MAP_LVDS666;
 	case MEDIA_BUS_FMT_BGR888_1X24:
 		return IPU_DC_MAP_BGR24;
-	default:
-		return -EINVAL;
 	}
 }
 
···
 	dc->di = ipu_di_get_num(di);
 
 	map = ipu_bus_format_to_map(bus_format);
-	BUG_ON(map < 0);
 
 	/*
 	 * In interlaced mode we need more counters to create the asymmetric