staging: rtl8723au: Validate keys in cfg80211_rtw_add_key()

We validate the parameters in cfg80211_rtw_add_key() so no need to do
it all again in rtw_cfg80211_{ap_}set_encryption()

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