mm/sharepool: Fix using uninitialized sp_flag

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5DS9S


CVE: NA

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Add the missing initialization for kc.sp_flag in
sp_make_share_kva_to_spg(). Or a random value would be used in
sp_remap_kva_to_vma().

Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>