[media] media drivers: annotate fall-through

Avoid warnings like those:

drivers/media/pci/ddbridge/ddbridge-core.c: In function 'dvb_input_detach':
drivers/media/pci/ddbridge/ddbridge-core.c:787:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
   if (input->fe) {
      ^
drivers/media/pci/ddbridge/ddbridge-core.c:792:2: note: here
  case 4:
  ^~~~
...

On several cases, it is just that gcc 7.1 is not capable of
understanding the comment, but on other places, we need an
annotation.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/gspca/ov519.c

@@ -3526,7 +3526,8 @@ static void ov511_mode_init_regs(struct sd *sd)
 				sd->clockdiv = 0;
 				break;
 			}
-			/* Fall through for 640x480 case */
+			/* For 640x480 case */
+			/* fall through */
 		default:
 /*		case 20: */
 /*		case 15: */