virtio-mem: Fix the iterator variable in a vmem->rdl_list loop

virtio-mem: Fix the iterator variable in a vmem->rdl_list loop

It should be the variable rdl2 to revert the already-notified listeners.

Fixes: 2044969f0b ("virtio-mem: Implement RamDiscardManager interface")
Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com>
Message-Id: <20221228090312.17276-1-chenyi.qiang@intel.com>
Cc: qemu-stable@nongnu.org
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
(cherry picked from commit 29f1b328e3b767cba2661920a8470738469b9e36)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>