migration: Fix typo in migrate_add_blocker() error message

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <155800428514.543845.17558475870097990036.stgit@bahia.lan>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

migration/migration.c

@@ -1728,7 +1728,7 @@ int migrate_add_blocker(Error *reason, Error **errp)
     if (only_migratable) {
         error_propagate_prepend(errp, error_copy(reason),
                                 "disallowing migration blocker "
-                                "(--only_migratable) for: ");
+                                "(--only-migratable) for: ");
         return -EACCES;
     }