net: phy: micrel: Fix PTP_PF_PEROUT for lan8841

If the 1PPS output was enabled and then lan8841 was configured to be a
follower, then target clock which is used to generate the 1PPS was not
configure correctly. The problem was that for each adjustments of the
time, also the nanosecond part of the target clock was changed.
Therefore the initial nanosecond part of the target clock was changed.
The issue can be observed if both the leader and the follower are
generating 1PPS and see that their PPS are not aligned even if the time
is allined.
The fix consists of not modifying the nanosecond part of the target
clock when adjusting the time. In this way the 1PPS get also aligned.

Fixes: e4ed8ba0 ("net: phy: micrel: Add support for PTP_PF_PEROUT for lan8841")
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>