IB/core: Fix port kobject deletion during error flow

When encountering an error during the add_port function, adding a port
to sysfs, the port kobject is freed without being deleted from sysfs.

Instead of freeing it directly, the patch uses kobject_put to release
the kobject and delete it.

Signed-off-by: Haggai Eran <haggaie@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>