USB: whiteheat: fix memory leak in error path

Make sure command buffer is deallocated in case of errors during attach.

Cc: <support@connecttech.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>