net/mlx5: Return correct EC_VF function ID

The ECVF function ID range is 1..max_ec_vfs. Currently
mlx5_vport_to_func_id returns 0..max_ec_vfs - 1. Which
results in a syndrome when querying the caps with more
recent firmware, or reading incorrect caps with older
firmware that supports EC VFs.

Fixes: 9ac0b128

 ("net/mlx5: Update vport caps query/set for EC VFs")
Signed-off-by: Daniel Jurgens <danielj@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>