Drop the request queue reference just acquired when __alloc_disk_node
failed.

Fixes: 6f8191fd ("block: simplify disk shutdown")
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Link: https://lore.kernel.org/r/20221122072753.426077-1-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>