ath9k: Configure AR_PHY_SWITCH_COM with apropriate antenna control

This fixes the poor wireless connection which happens even
if we are very well in the range.

Signed-off-by:  <Don.breslin@atheros.com>
Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>