ath9k: Remove ath_ant_comb_update()

During a HW reset, the diversity config is programmed
in the set_board_values() eeprom callback, there is no
need to do it again by calling ath_ant_comb_update().

Fixed antenna support is not fully handled for 1-stream
cards, it can be done later.

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