[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/dvb-frontends/bcm3510.c

@@ -773,7 +773,8 @@ static int bcm3510_init(struct dvb_frontend* fe)
 			deb_info("attempting to download firmware\n");
 			if ((ret = bcm3510_init_cold(st)) < 0)
 				return ret;
-		case JDEC_EEPROM_LOAD_WAIT: /* fall-through is wanted */
+			/* fall-through */
+		case JDEC_EEPROM_LOAD_WAIT:
 			deb_info("firmware is loaded\n");
 			bcm3510_check_firmware_version(st);
 			break;