rt2x00: rt2800: increase EEPROM_SIZE to 512 bytes

Ralink 3T chipsets are using a different EEPROM
layout than the others. The EEPROM on these devices
contain more data than the others which does not fit
into 272 byte which the rt2800 driver actually uses.

The Ralink reference driver defines EEPROM_SIZE to
512/1024 bytes for PCI/USB devices respectively.

Increase the EEPROM_SIZE constant to 512 bytes, in
order to make room for EEPROM data of 3T devices.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Acked-by: Helmut Schaa <helmut.schaa@googlemail.com>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>