qapi: Convert migrate_cancel

Signed-off-by: Luiz Capitulino <[email protected]>
diff --git a/migration.c b/migration.c
index 8280d71..fa603d6 100644
--- a/migration.c
+++ b/migration.c
@@ -468,10 +468,9 @@
     return 0;
 }
 
-int do_migrate_cancel(Monitor *mon, const QDict *qdict, QObject **ret_data)
+void qmp_migrate_cancel(Error **errp)
 {
     migrate_fd_cancel(migrate_get_current());
-    return 0;
 }
 
 int do_migrate_set_speed(Monitor *mon, const QDict *qdict, QObject **ret_data)