staging: r8723au: Fix randconfig build errors

staging: r8723au: Fix randconfig build errors

The kbuild test robot got the following errors for i386-randconfig-c0-04060652:

ERROR: "wiphy_free" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "bridge_tunnel_header" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "ieee80211_frequency_to_channel" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "cfg80211_rx_mgmt" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "ieee80211_channel_to_frequency" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "cfg80211_mgmt_tx_status" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "rfc1042_header" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "__ieee80211_get_channel" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "wiphy_unregister" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "cfg80211_connect_result" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "cfg80211_michael_mic_failure" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "cfg80211_roamed" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "cfg80211_put_bss" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "wiphy_new" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "wiphy_register" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "cfg80211_inform_bss_width_frame" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "cfg80211_disconnected" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "ieee80211_amsdu_to_8023s" [drivers/staging/rtl8723au/r8723au.ko] undefined!
ERROR: "cfg80211_scan_done" [drivers/staging/rtl8723au/r8723au.ko] undefined!

All of these are fixed by forcing the selection of CFG80211 in Kconfig.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Jes Sorensen <Jes.Sorensen@redhat.com>
Cc: kbuild-all@01.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>