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: 3f2c045022e8 ("ptp: ocp: Add ptp_ocp_adjtime_coarse for large adjustments")
Suggested-by: Vadim Fedorenko <vfedorenko@novek.ru>
Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Acked-by: Vadim Fedorenko <vfedorenko@novek.ru>
Link: https://lore.kernel.org/r/20220513225231.1412-1-jonathan.lemon@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>