mm: mem_reliable: Fix blank space issue in reliable_report_usage()

hulk inclusion
category: cleanup
bugzilla: https://gitee.com/openeuler/kernel/issues/I6WKXZ


CVE: NA

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The blank space before kB is needed to align the previous memory report
style.

Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>