net: hns3: unsigned value not need to judge to be less than 0

driver inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8PDAE


CVE: NA

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Fixes: c64545e1 ("net: hns3: add support for Hisilicon ptp sync device")
Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>