time: Normalize timespec64 before timespec64_compare()

hulk inclusion
category: bugfix
bugzilla: 185831, https://gitee.com/openeuler/kernel/issues/I4MO2G


CVE: NA

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Passing unnormalized timespec64 to timespec64_compare() may cause
incorrect results.

For example:
  wall_to_monotonic = {tv_sec = -10, tv_nsec = 900000000}
  ts_delta = {tv_sec = -9, tv_nsec = -900000000}

timespec64_compare() returns -1, but actually wall_to_monotonic > ts_delta.
This will cause wall_to_monotonic to become a positive number.

Use timespec64_sub() instead of direct subtraction to avoid this.

Signed-off-by: Yu Liao <liaoyu15@huawei.com>
Reviewed-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>