scsi: sd: Clean up gendisk if device_add_disk() failed

We forgot to call blk_cleanup_disk() when device_add_disk() failed.  This
would cause a memory leak of gendisk and sched_tags allocated in
elevator_init_mq()

Reference:https://syzkaller.appspot.com/x/log.txt?x=13b41dcb700000
Reported-and-tested-by:  <syzbot+f08c77040fa163a75a46@syzkaller.appspotmail.com>
Link: https://lore.kernel.org/r/20220401011018.1026553-1-haowenchao@huawei.com
Signed-off-by: Wenchao Hao <haowenchao@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>