staging: rtl8712: check copy_from_user return value

Description:return -EFAULT if copy_to_user() fails

Signed-off-by: Xiaochen Wang <wangxiaochen0@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>