RDMA/core: Fix panic when port_data isn't initialized

RDMA/core: Fix panic when port_data isn't initialized

This happens if assign_name() returns failure when called from
ib_register_device(), that will lead to the following panic in every time
that someone touches the port_data's data members.

 BUG: unable to handle kernel NULL pointer dereference at 00000000000000c0
 PGD 0 P4D 0
 Oops: 0002 [#1] SMP PTI
 CPU: 19 PID: 1994 Comm: systemd-udevd Not tainted 5.1.0-rc5+ #1
 Hardware name: HP ProLiant DL360p Gen8, BIOS P71 12/20/2013
 RIP: 0010:_raw_spin_lock_irqsave+0x1e/0x40
 Code: 85 ff 66 2e 0f 1f 84 00 00 00 00 00 66 66 66 66 90 53 9c 58 66 66 90
 66 90 48 89 c3 fa 66 66 90 66 66 90 31 c0 ba 01 00 00 00 <f0> 0f b1 17 0f
 94 c2 84 d2 74 05 48 89 d8 5b c3 89 c6 e8 b4 85 8a
 RSP: 0018:ffffa8d7079a7c08 EFLAGS: 00010046
 RAX: 0000000000000000 RBX: 0000000000000202 RCX: ffffa8d7079a7bf8
 RDX: 0000000000000001 RSI: ffff93607c990000 RDI: 00000000000000c0
 RBP: 0000000000000001 R08: 0000000000000000 R09: ffffffffc08c4dd8
 R10: 0000000000000000 R11: 0000000000000001 R12: 00000000000000c0
 R13: ffff93607c990000 R14: ffffffffc05a9740 R15: ffffa8d7079a7e98
 FS:  00007f1c6ee438c0(0000) GS:ffff93609f6c0000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00000000000000c0 CR3: 0000000819fca002 CR4: 00000000000606e0
 Call Trace:
  free_netdevs+0x4d/0xe0 [ib_core]
  ib_dealloc_device+0x51/0xb0 [ib_core]
  __mlx5_ib_add+0x5e/0x70 [mlx5_ib]
  mlx5_add_device+0x57/0xe0 [mlx5_core]
  mlx5_register_interface+0x85/0xc0 [mlx5_core]
  ? 0xffffffffc0474000
  do_one_initcall+0x4e/0x1d4
  ? _cond_resched+0x15/0x30
  ? kmem_cache_alloc_trace+0x15f/0x1c0
  do_init_module+0x5a/0x218
  load_module+0x186b/0x1e40
  ? m_show+0x1c0/0x1c0
  __do_sys_finit_module+0x94/0xe0
  do_syscall_64+0x5b/0x180
  entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: 8ceb1357b337 ("RDMA/device: Consolidate ib_device per_port data into one place")
Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>