staging: rtl8723au: rtw_get_bcn_info23a(): Use capability from wlan_bssid_ex

This eliminates yet another user of rtw_get_capability23a_from_ie()

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>