isdn: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Warning level 2 was used: -Wimplicit-fallthrough=2

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/hardware/mISDN/mISDNinfineon.c

@@ -887,6 +887,7 @@ release_card(struct inf_hw *card) {
 				release_card(card->sc[i]);
 			card->sc[i] = NULL;
 		}
+		/* fall through */
 	default:
 		pci_disable_device(card->pdev);
 		pci_set_drvdata(card->pdev, NULL);