net/mlx5e: Fix wrong field name in FEC related functions

This bug would result in reading wrong FEC capabilities for 10G/40G.

Fixes: 2095b264

 ("net/mlx5e: Add port FEC get/set functions")
Signed-off-by: Shay Agroskin <shayag@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>