net: hns3: change the method of obtaining default ptp cycle

mainline inclusion
from mainline-master
commit 8373cd38
category: bugfix
bugzilla: 173966
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8373cd38a8888549ace7c7617163a2e826970a92



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The ptp cycle is related to the hardware, so it may cause compatibility
issues if a fixed value is used in driver. Therefore, the method of
obtaining this value is changed to read from the register rather than
use a fixed value in driver.

Fixes: 0bf5eb78 ("net: hns3: add support for PTP")
Signed-off-by: Yufeng Mo <moyufeng@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Reviewed-by: Yongxin Li <liyongxin1@huawei.com>
Signed-off-by: Junxin Chen <chenjunxin1@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>