staging: rtl8723au: rtw_cfg80211_ap_set_encryption(): Use key_params->cipher to determine encryption

Passing strings around for something we have defines for is just
silly.
Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>