wl12xx: fix kconfig/link errors

"boolean" converts a module dependency (MAC80211=m) to YES,
then the WL12XX driver can be built-in instead of only
modular, which leads to linker errors:

wl1271_main.c:(.text+0x11177d): undefined reference to `ieee80211_frequency_to_channel'
wl1271_main.c:(.text+0x111adc): undefined reference to `ieee80211_stop_queues'
wl1271_main.c:(.text+0x112005): undefined reference to `ieee80211_scan_completed'
(.text+0x1139c8): undefined reference to `ieee80211_scan_completed'
(.text+0x113bb0): undefined reference to `ieee80211_tx_status'
(.text+0x113e53): undefined reference to `ieee80211_stop_queues'
(.text+0x113e8d): undefined reference to `ieee80211_wake_queues'
(.text+0x113f3b): undefined reference to `ieee80211_tx_status'
(.text+0x113f60): undefined reference to `ieee80211_tx_status'
(.text+0x1140f0): undefined reference to `ieee80211_channel_to_frequency'
(.text+0x114153): undefined reference to `ieee80211_rx'
wl1271_main.c:(.devinit.text+0xca08): undefined reference to `ieee80211_alloc_hw'
wl1271_main.c:(.devinit.text+0xccf5): undefined reference to `ieee80211_register_hw'
wl1271_main.c:(.devinit.text+0xcd6b): undefined reference to `ieee80211_free_hw'
wl1271_main.c:(.devexit.text+0x1353): undefined reference to `ieee80211_unregister_hw'
wl1271_main.c:(.devexit.text+0x13c9): undefined reference to `ieee80211_free_hw'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/wl12xx/Kconfig

@@ -1,5 +1,5 @@
 menuconfig WL12XX
-	boolean "TI wl12xx driver support"
+	tristate "TI wl12xx driver support"
 	depends on MAC80211 && WLAN_80211 && EXPERIMENTAL
 	---help---
 	  This will enable TI wl12xx driver support. The drivers make