input: fix memory leak

If kbd_queue is not empty and queue_count >= queue_limit,
we should free evt.

Change-Id: Ieeacf90d5e7e370a40452ec79031912d8b864d83
Signed-off-by: linzhecheng <linzhecheng@huawei.com>
Message-id: 20171225023730.5512-1-linzhecheng@huawei.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
