staging: rtl8723au: rtw_cfg80211_ap_set_encryption(): Use keyparms->cipher to set WEP size

We already know which type of WEP we are using when we get here, no
point trying to determine it from key_len.

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