ath9k_hw: Fix eeprom offset for AR9287 devices (PCI/USB)

AR9287 devices (PCI/USB) use different eeprom start location
to read nvram. New devices might endup with same devid. So use
driver_info to set offset, instead of devid. driver_info is
valid for HTC devices alone which is filled in usb_device_id.

Signed-off-by: Rajkumar Manoharan <rmanoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>