ath: depend on cfg80211

The ath.ko module itself depends on cfg80211
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/Kconfig

 config ATH_COMMON
 	tristate "Atheros Wireless Cards"
 	depends on WLAN_80211
+	depends on CFG80211
 	depends on ATH5K || ATH9K || AR9170_USB
 
 source "drivers/net/wireless/ath/ath5k/Kconfig"