IB/core: A small refactor in destroy WQ handler

Instead of having uverbs_uobject_put both in the error flow and the
good flow, we unite them.

Fixes: fd3c7904 ('IB/core: Change idr objects to use the new schema')
Signed-off-by: Matan Barak <matanb@mellanox.com>
Reviewed-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>