Fix missing break, causing sigprocmask(SIG_SETMASK ...) to always

return an error.

Interestingly, nobody much seems to care. Apparently few programs
check the error value.

kernel/signal.c

@@ -1611,6 +1611,7 @@ int sigprocmask(int how, sigset_t *set, sigset_t *oldset)
 		break;
 	case SIG_SETMASK:
 		current->blocked = *set;
+		break;
 	default:
 		error = -EINVAL;
 	}