rt2x00: Align rt2800 EEPROM validation to Ralink vendor driver.

Align with the latest versions of the Ralink legacy driver(s).

Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>