[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>
diff --git a/drivers/media/dvb-frontends/mt352.c b/drivers/media/dvb-frontends/mt352.c
index e127090..d5fa96f 100644
--- a/drivers/media/dvb-frontends/mt352.c
+++ b/drivers/media/dvb-frontends/mt352.c
@@ -211,6 +211,7 @@
 			if (op->hierarchy == HIERARCHY_AUTO ||
 			    op->hierarchy == HIERARCHY_NONE)
 				break;
+			/* fall through */
 		default:
 			return -EINVAL;
 	}