thunderbolt: Use the actual buffer in tb_async_error()

The received notification packet is held in pkg->buffer and not in pkg
itself. Fix this by using the correct buffer.

Fixes: 81a54b5e

 ("thunderbolt: Let the connection manager handle all notifications")
Cc: stable@vger.kernel.org
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>