[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/i2c/msp3400-kthreads.c

@@ -655,6 +655,7 @@ restart:
 			break;
 		case 0: /* 4.5 */
 			state->detected_std = V4L2_STD_MN;
+			/* fall-through */
 		default:
 no_second:
 			state->second = msp3400c_carrier_detect_main[max1].cdo;