thunderbolt: Fix memory leak in tb_handle_dp_bandwidth_request()

The memory allocated in tb_queue_dp_bandwidth_request() needs to be
released once the request is handled to avoid leaking it.

Fixes: 6ce35635 ("thunderbolt: Add support for DisplayPort bandwidth allocation mode")
Cc: stable@vger.kernel.org
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>