staging: rtl8723au: Use struct ieee80211_mcs_info to describe MCS information

The original RTL code defined the MCS information as a 16 byte array
and blindly applied it's masking over the full array, ignoring the
fact that only the first 10 bytes describe the rx_mask and the rest
are different fields.

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