block: call bdput() to avoid memleak

hulk inclusion
category: bugfix
bugzilla: 109288
CVE: NA

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bdget_disk() will get bd_inode, so it need to do bdput().

Fixes: 3ad15d050daa ("block: take bd_mutex around delete_partitions in del_gendisk")
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>