NET: asix: fix ethtool -e for AX88178 USB dongle

"ethtool -e ethX" dumps EEPROM data. Patch sets EEPROM length for device.
Ethtool works alot better when the kernel believes the length is > 0.

From: Allan Chou <allan@asix.com.tw>
Signed-off-by: Grant Grundler <grundler@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>