RDMA/core: Fix null-ptr-deref in ib_core_cleanup()

KASAN reported a null-ptr-deref error:

  KASAN: null-ptr-deref in range [0x0000000000000118-0x000000000000011f]
  CPU: 1 PID: 379
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
  RIP: 0010:destroy_workqueue+0x2f/0x740
  RSP: 0018:ffff888016137df8 EFLAGS: 00000202
  ...
  Call Trace:
   ib_core_cleanup+0xa/0xa1 [ib_core]
   __do_sys_delete_module.constprop.0+0x34f/0x5b0
   do_syscall_64+0x3a/0x90
   entry_SYSCALL_64_after_hwframe+0x63/0xcd
  RIP: 0033:0x7fa1a0d221b7
  ...

It is because the fail of roce_gid_mgmt_init() is ignored:

 ib_core_init()
   roce_gid_mgmt_init()
     gid_cache_wq = alloc_ordered_workqueue # fail
 ...
 ib_core_cleanup()
   roce_gid_mgmt_cleanup()
     destroy_workqueue(gid_cache_wq)
     # destroy an unallocated wq

Fix this by catching the fail of roce_gid_mgmt_init() in ib_core_init().

Fixes: 03db3a2d

 ("IB/core: Add RoCE GID table management")
Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
Link: https://lore.kernel.org/r/20221025024146.109137-1-chenzhongjin@huawei.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>