net/mlx5: Add error prints when validate ETS failed

Upon set ETS failure due to user invalid input, add error prints to
specify the exact error to the user.

Fixes: cdcf1121 ('net/mlx5e: Validate BW weight values of ETS')
Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>