ath5k: fix the EEPROM check for hw AES crypto support

EEPROM version 5.0 adds a new field for disabling AES support, having
an older version means that AES is present. This patch fixes hw AES
crypto support on AR5312 boards, which have an older EEPROM version.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>