staging: r8188eu: use a qos_hdr in validate_recv_data_frame

Define a struct ieee80211_qos_hdr in the validate_recv_data_frame
function. Use this struct to replace some numeric offsets and make the
code easier to understand.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20221107202824.61431-2-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>