ptp: ocp: have adjtime handle negative delta_ns correctly

ptp: ocp: have adjtime handle negative delta_ns correctly

delta_ns is a s64, but it was being passed ptp_ocp_adjtime_coarse
as an u64.  Also, it turns out that timespec64_add_ns() only handles
positive values, so perform the math with set_normalized_timespec().

Fixes: 90f8f4c0e3ce ("ptp: ocp: Add ptp_ocp_adjtime_coarse for large adjustments")
Suggested-by: Vadim Fedorenko <[email protected]>
Signed-off-by: Jonathan Lemon <[email protected]>
Acked-by: Vadim Fedorenko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>