rtl8187: Remove deprecated 'qual' from returned RX status

The qual member of ieee80211_rx_status is deprecated. As a result, this
driver no longer needs to calculate a quality value.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Acked-by: Hin-Tak Leung <htl10@users.sourceforge.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>