staging: fix ath6kl build when CFG80211 is not enabled

Fix build errors when CONFIG_CFG80211 is not enabled:

drivers/built-in.o: In function `ar6k_cfg80211_deinit':
(.text+0x189b71): undefined reference to `cfg80211_scan_done'
drivers/built-in.o: In function `ar6k_cfg80211_deinit':
(.text+0x189b86): undefined reference to `wiphy_unregister'
drivers/built-in.o: In function `ar6k_cfg80211_deinit':
(.text+0x189b8d): undefined reference to `wiphy_free'
drivers/built-in.o: In function `ar6k_cfg80211_init':
(.text+0x18add7): undefined reference to `wiphy_new'
drivers/built-in.o: In function `ar6k_cfg80211_init':
(.text+0x18ae48): undefined reference to `wiphy_register'
drivers/built-in.o: In function `ar6k_cfg80211_tkip_micerr_event':
(.text+0x18ae95): undefined reference to `cfg80211_michael_mic_failure'
drivers/built-in.o: In function `ar6k_cfg80211_scan_node':
(.text+0x18afb5): undefined reference to `__ieee80211_get_channel'
drivers/built-in.o: In function `ar6k_cfg80211_scan_node':
(.text+0x18afd2): undefined reference to `cfg80211_inform_bss_frame'
drivers/built-in.o: In function `ar6k_cfg80211_disconnect_event':
(.text+0x18b046): undefined reference to `cfg80211_ibss_joined'
drivers/built-in.o: In function `ar6k_cfg80211_disconnect_event':
(.text+0x18b176): undefined reference to `cfg80211_connect_result'
drivers/built-in.o: In function `ar6k_cfg80211_disconnect_event':
(.text+0x18b190): undefined reference to `cfg80211_disconnected'
drivers/built-in.o: In function `ar6k_cfg80211_connect_event':
(.text+0x18b291): undefined reference to `cfg80211_get_bss'
drivers/built-in.o: In function `ar6k_cfg80211_connect_event':
(.text+0x18b457): undefined reference to `cfg80211_put_bss'
drivers/built-in.o: In function `ar6k_cfg80211_connect_event':
(.text+0x18b4fa): undefined reference to `cfg80211_roamed'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Luis R. Rodriguez <mcgrof@gmail.com>
Cc: Joe Perches <joe@perches.com>
Cc: Naveen Singh <nsingh@atheros.com>
Signed-off-by: Peter Foley <pefoley2@verizon.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>