share_pool: don't trace the invalid spa address

ascend inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4M23J


CVE: NA

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Don't use the spa's va_start if the spa is not valid.

Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>