atheros: define a common priv struct

hw code should never use private driver data, but
sometimes we need a backpointer so just stuff it on
the common ath struct.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/hw.h

@@ -450,7 +450,6 @@ struct ath_gen_timer_table {
 
 struct ath_hw {
 	struct ieee80211_hw *hw;
-	struct ath_softc *ah_sc;
 	struct ath_common common;
 	struct ath9k_hw_version hw_version;
 	struct ath9k_ops_config config;