libertas: depend on CONFIG_CFG80211

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/libertas/Kconfig

 config LIBERTAS
 	tristate "Marvell 8xxx Libertas WLAN driver support"
-	depends on WLAN_80211
+	depends on WLAN_80211 && CFG80211
 	select WIRELESS_EXT
 	select WEXT_SPY
 	select LIB80211