ath9k_hw: Set proper eeprom offset for AR9287 HTC devices

AR9287 based PCI & USB devices are differed in eeprom start offset.
So set proper the offset for HTC devices to read nvram correctly.

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