ath9k: Remove ATH9K_HW_WOW_DEVICE_CAPABLE

Enabling WOW based on the chip is incorrect since
it needs to be done for specific sub-devices which
have proper platform support.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>