s390/mm: 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>

arch/s390/mm/fault.c

@@ -852,9 +852,7 @@ void do_secure_storage_access(struct pt_regs *regs)
 			BUG();
 		break;
 	case VDSO_FAULT:
-		/* fallthrough */
 	case GMAP_FAULT:
-		/* fallthrough */
 	default:
 		do_fault_error(regs, VM_READ | VM_WRITE, VM_FAULT_BADMAP);
 		WARN_ON_ONCE(1);