ath9k_hw: support reading calibration data from flash on AR9003

Embedded boards do not have compressed EEPROM data, they use the
struct ar9003_eeprom layout, with little endian fields, so copying
the raw data to the eeprom buffer is enough.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>