kconfig: annotate non-trivial fall-trough

Signed-off-by: Arnaud Lacombe <lacombar@gmail.com>
diff --git a/scripts/kconfig/mconf.c b/scripts/kconfig/mconf.c
index d433c7a..87001e6 100644
--- a/scripts/kconfig/mconf.c
+++ b/scripts/kconfig/mconf.c
@@ -845,6 +845,7 @@
 				"\n\n"));
 			return 1;
 		}
+		/* fall through */
 	case -1:
 		printf(_("\n\n"
 			"*** End of the configuration.\n"