s390/vfio: use fallthrough;

Convert the various uses of fallthrough comments to fallthrough;

Done via script
Link: https://lore.kernel.org/lkml/b56602fcf79f849e733e7b521bb0e17895d390fa.1582230379.git.joe.com/Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

drivers/s390/crypto/vfio_ap_ops.c

@@ -90,7 +90,7 @@ static void vfio_ap_wait_for_irqclear(int apqn)
 		case AP_RESPONSE_RESET_IN_PROGRESS:
 			if (!status.irq_enabled)
 				return;
-			/* Fall through */
+			fallthrough;
 		case AP_RESPONSE_BUSY:
 			msleep(20);
 			break;