net: ks8851: Drop eeprom_size structure member

After commit 51b7b1c3 (KSZ8851-SNL: Add ethtool support for
EEPROM via eeprom_93cx6, 2011-11-21) this structure member is
unused. Delete it.

Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>