omapfb: Mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

drivers/video/fbdev/omap2/omapfb/omapfb-main.c

@@ -893,6 +893,7 @@ int omapfb_setup_overlay(struct fb_info *fbi, struct omap_overlay *ovl,
 				/ (var->bits_per_pixel >> 2);
 			break;
 		}
+		/* fall through */
 	default:
 		screen_width = fix->line_length / (var->bits_per_pixel >> 3);
 		break;