net/mlx5e: Removed unnecessary warnings in FEC caps query

Querying interface FEC caps with 'ethtool [int]' after link reset
throws warning regading link speed.
This warning is not needed as there is already an indication in
user space that the link is not up.

Fixes: 0696d608

 ("net/mlx5e: Receive buffer configuration")
Signed-off-by: Shay Agroskin <shayag@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>