staging: wlan-ng: fix ODEBUG bug in prism2sta_disconnect_usb

We should cancel hw->usb_work before kfree(hw).

Reported-by: syzbot+6d2e7f6fa90e27be9d62@syzkaller.appspotmail.com
Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/1585120006-30042-1-git-send-email-hqjagain@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wlan-ng/prism2usb.c

@@ -180,6 +180,7 @@ static void prism2sta_disconnect_usb(struct usb_interface *interface)
 
 		cancel_work_sync(&hw->link_bh);
 		cancel_work_sync(&hw->commsqual_bh);
+		cancel_work_sync(&hw->usb_work);
 
 		/* Now we complete any outstanding commands
 		 * and tell everyone who is waiting for their