staging: r8712u: Use 802.11bg mode to make a WEP connection

There are some IOT issues when 802.11bgn mode is used to make a WEP
connection.

Signed-off-by: Albert Wang <albert_wang@realtek.com.tw>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>