net/mlx5e: ethtool, Remove unsupported SFP EEPROM high pages query

Querying EEPROM high pages data for SFP module is currently
not supported by our driver and yet queried, resulting in
invalid FW queries.

Set the EEPROM ethtool data length to 256 for SFP module will
limit the reading for page 0 only and prevent invalid FW queries.

Fixes: bb64143e

 ("net/mlx5e: Add ethtool support for dump module EEPROM")
Signed-off-by: Erez Alfasi <ereza@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>