ath9k_htc: fix eeprom access

wireless-testing commit a05b5d45
ath9k: add support for reading eeprom from platform data on PCI devices

This change moved the initialization of the AH_USE_EEPROM flag from ath9k_hw
to ath9k. This needs to be added to ath9k_htc as well

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