[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/usb/pwc/pwc-v4l.c b/drivers/media/usb/pwc/pwc-v4l.c
index 92f04db..043b2b9 100644
--- a/drivers/media/usb/pwc/pwc-v4l.c
+++ b/drivers/media/usb/pwc/pwc-v4l.c
@@ -568,7 +568,8 @@ static int pwc_g_volatile_ctrl(struct v4l2_ctrl *ctrl)
 		pdev->gain_valid = true;
 		if (!DEVICE_USE_CODEC3(pdev->type))
 			break;
-		/* Fall through for CODEC3 where autogain also controls expo */
+		/* For CODEC3 where autogain also controls expo */
+		/* fall through */
 	case V4L2_CID_EXPOSURE_AUTO:
 		if (pdev->exposure_valid && time_before(jiffies,
 				pdev->last_exposure_update + HZ / 4)) {