etmem_scan: fix memleak in vm_idle_read

euleros inclusion
category: bugfix
bugzilla: NA

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Struct page_idle_ctrl is alloced at beginning of vm_idle_read, but
it's not freed when vm_idle_read ends.

Fixes: bad4d883 ("etmem: add etmem-scan feature")
Signed-off-by: Kemeng Shi <shikemeng@huawei.com>
Reviewed-by: Jing <Xiangfeng&lt;jingxiangfeng@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>