tests/qtest: Fix typo in multifd cancel test

This wasn't noticed because the test is currently disabled.

Fixes: 02f56e3de ("tests/qtest: massively speed up migration-test")
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <20230711212131.2370-1-farosas@suse.de>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

tests/qtest/migration-test.c

@@ -2481,7 +2481,7 @@ static void test_multifd_tcp_cancel(void)
 
     migrate_qmp(from, uri, "{}");
 
-    migrate_wait_for_dirty_mem(from, to);
+    migrate_wait_for_dirty_mem(from, to2);
 
     migrate_ensure_converge(from);