staging: rtl8712: Remove unused CamelCase define

* Remove unused CamelCase in order to get rid of the corresponding
  checkpatch.pl "CHECK: Avoid CamelCase: <IEEE80211_QoS_DATAGRP>"

Signed-off-by: Michael Hornung <mhornung.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>