net/mlx5: Add .getmaxphase ptp_clock_info callback

Implement .getmaxphase callback of ptp_clock_info in mlx5 driver. No longer
do a range check in .adjphase callback implementation. Handled by the ptp
stack.

Cc: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>