blk-mq: fix possible memleak when register 'hctx' failed

In the Linux kernel, the following vulnerability has been resolved:

blk-mq: fix possible memleak when register 'hctx' failed

There's issue as follows when do fault injection test:
unreferenced object 0xffff888132a9f400 (size 512):
comm "insmod", pid 308021, jiffies 4324277909 (age 509.733s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 08 f4 a9 32 81 88 ff ff ...........2....
08 f4 a9 32 81 88 ff ff 00 00 00 00 00 00 00 00 ...2............
backtrace:
[<00000000e8952bb4>] kmalloc_node_trace+0x22/0xa0
[<00000000f9980e0f>] blk_mq_alloc_and_init_hctx+0x3f1/0x7e0
[<000000002e719efa>] blk_mq_realloc_hw_ctxs+0x1e6/0x230
[<000000004f1fda40>] blk_mq_init_allocated_queue+0x27e/0x910
[<00000000287123ec>] __blk_mq_alloc_disk+0x67/0xf0
[<00000000a2a34657>] 0xffffffffa2ad310f
[<00000000b173f718>] 0xffffffffa2af824a
[<0000000095a1dabb>] do_one_initcall+0x87/0x2a0
[<00000000f32fdf93>] do_init_module+0xdf/0x320
[<00000000cbe8541e>] load_module+0x3006/0x3390
[<0000000069ed1bdb>] __do_sys_finit_module+0x113/0x1b0
[<00000000a1a29ae8>] do_syscall_64+0x35/0x80
[<000000009cd878b0>] entry_SYSCALL_64_after_hwframe+0x46/0xb0

Fault injection context as follows:
kobject_add
blk_mq_register_hctx
blk_mq_sysfs_register
blk_register_queue
device_add_disk
null_add_dev.part.0 [null_blk]

As 'blk_mq_register_hctx' may already add some objects when failed halfway,
but there isn't do fallback, caller don't know which objects add failed.
To solve above issue just do fallback when add objects failed halfway in
'blk_mq_register_hctx'.