thunderbolt: Call tb_switch_put() once DisplayPort bandwidth request is finished

When handling DisplayPort bandwidth request tb_switch_find_by_route() is
called and it returns a router structure with reference count increased.
In order to avoid resource leak call tb_switch_put() when finished.

Fixes: 6ce35635

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