USB: rio500: fix memory leak in close after disconnect

If a disconnected device is closed, rio_close() must free
the buffers.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>