monitor: fix the wrong order of releasing keys

(qemu) sendkey ctrl_r-scroll_lock-scroll_lock

Executing this command could not let Windows guest panic, it caused by
the wrong order of releasing keys. This problem was introduced by
commit e4c8f004c55d9da3eae3e14df740238bf805b5d6.

The right release order should be starting from last item.

Signed-off-by: Amos Kong <akong@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
