this is necessary to support Antenna diversity and combining in new chip
sets such as AR9485, previously Antenna diversity support is available
only in AR9285

Cc: Gabriel Tseng <Gabriel.Tseng@Atheros.com>
Cc: Senthilkumar Balasubramanian <Senthilkumar.Balasubramanian@Atheros.com>
Signed-off-by: NMohammed Shafi Shajakhan <mshajakhan@atheros.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>