staging: rtl8723au: rtw_check_bcn_info23a(): Don't make a local copy of beacon just to parse it

In addition be consistent with return values and parsing them.

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