scftorture: Check unexpected "switch" statement value

This commit adds a "default" case to the switch statement in
scftorture_invoke_one() which contains a WARN_ON_ONCE() and an assignment
to ->scfc_out to suppress knock-on warnings.  These knock-on warnings
could otherwise cause the user to think that there was a memory-ordering
problem in smp_call_function() instead of a bug in scftorture.c itself.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/scftorture.c

@@ -357,6 +357,10 @@ static void scftorture_invoke_one(struct scf_statistics *scfp, struct torture_ra
 		}
 		smp_call_function(scf_handler, scfcp, scfsp->scfs_wait);
 		break;
+	default:
+		WARN_ON_ONCE(1);
+		if (scfcp)
+			scfcp->scfc_out = true;
 	}
 	if (scfcp && scfsp->scfs_wait) {
 		if (WARN_ON_ONCE(!scfcp->scfc_out))