wireless: fix Atheros drivers compilation

Bug introduced in commit:
wireless: allow Atheros card to not depend on ath.ko

Commit in question changed CONFIG_ATH_COMMON to CONFIG_ATH_CARDS as
"Atheros card" indication in drivers/net/wireless/ath/Kconfig but it
is used also by drivers/net/wireless/Makefile

If there are only Atheros cards that do not require ATH_COMMON, whole
Makefile for Atheros cards was not executed; and as result, driver
won't compile in this case.

Change in CONFIG_ option name should be reflected in the
drivers/net/wireless/Makefile

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Tested-by: Kalle Valo <kvalo@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/Makefile

@@ -47,7 +47,7 @@ obj-$(CONFIG_RT2X00)	+= rt2x00/
 
 obj-$(CONFIG_P54_COMMON)	+= p54/
 
-obj-$(CONFIG_ATH_COMMON)	+= ath/
+obj-$(CONFIG_ATH_CARDS)		+= ath/
 
 obj-$(CONFIG_MAC80211_HWSIM)	+= mac80211_hwsim.o