net/mlx5e: Correct the calculation of max channels for rep

Correct the calculation of maximum channels of rep to better utilize
the hardware resources and allow a larger scale of reps.

This will allow creation of all virtual ports configured.

Fixes: 473baf2e

 ("net/mlx5e: Allow profile-specific limitation on max num of channels")
Signed-off-by: Moshe Tal <moshet@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>