staging: rtl8723au: OnAssocReq23a(): Simplify parsing crypto info from the IE

This reduces the dependency of rtw_ieee802_11_parse_elems23a() which
is only used in this function. Follow-on patches will remove the
remaining dependencies and get rid of the function.

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