[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/usb/usbvision/usbvision-i2c.c

@@ -311,10 +311,13 @@ usbvision_i2c_read_max4(struct usb_usbvision *usbvision, unsigned char addr,
 	switch (len) {
 	case 4:
 		buf[3] = usbvision_read_reg(usbvision, USBVISION_SER_DAT4);
+		/* fall through */
 	case 3:
 		buf[2] = usbvision_read_reg(usbvision, USBVISION_SER_DAT3);
+		/* fall through */
 	case 2:
 		buf[1] = usbvision_read_reg(usbvision, USBVISION_SER_DAT2);
+		/* fall through */
 	case 1:
 		buf[0] = usbvision_read_reg(usbvision, USBVISION_SER_DAT1);
 		break;