net/mlx5: DPLL, Implement fractional frequency offset get pin op

Implement ffo_get() pin op filling it up to MSEED.frequency_diff value.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Acked-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Acked-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Link: https://lore.kernel.org/r/20240103132838.1501801-4-jiri@resnulli.us


Signed-off-by: Jakub Kicinski <kuba@kernel.org>