block: fix kobject leak in blk_unregister_queue

The kobject for the queue, `disk->queue_kobj`, is initialized with a
reference count of 1 via `kobject_init()` in `blk_register_queue()`.
While `kobject_del()` is called during the unregister path to remove
the kobject from sysfs, the initial reference is never released.

Add a call to `kobject_put()` in `blk_unregister_queue()` to properly
decrement the reference count and fix the leak.

Fixes: 2bd8522 ("block: untangle request_queue refcounting from sysfs")
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250711083009.2574432-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Ming Lei

block/blk-sysfs.c

@@ -960,4 +960,5 @@ void blk_unregister_queue(struct gendisk *disk)
 		elevator_set_none(q);
 
 	blk_debugfs_remove(disk);
+	kobject_put(&disk->queue_kobj);
 }