ath9k: Bypass EEPROM for diversity cap for AR9565

Use a default antenna diversity value for AR9565 instead
of relying on the EEPROM/OTP programmed value.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>