[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/rc/iguanair.c

@@ -113,6 +113,7 @@ static void process_ir_data(struct iguanair *ir, unsigned len)
 			break;
 		case CMD_TX_OVERFLOW:
 			ir->tx_overflow = true;
+			/* fall through */
 		case CMD_RECEIVER_OFF:
 		case CMD_RECEIVER_ON:
 		case CMD_SEND: