ath9k: Enable Fractional N mode

This patch enables Fractional N mode for all channel
if the EEPROM says so, and also fixes the INI only
when the device is not a 2 GHz only capable device.

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