IB/hfi1: Fix early init panic

The following trace can be observed with an init failure such as firmware
load failures:

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
  PGD 0 P4D 0
  Oops: 0010 [#1] SMP PTI
  CPU: 0 PID: 537 Comm: kworker/0:3 Tainted: G           OE    --------- -  - 4.18.0-240.el8.x86_64 #1
  Workqueue: events work_for_cpu_fn
  RIP: 0010:0x0
  Code: Bad RIP value.
  RSP: 0000:ffffae5f878a3c98 EFLAGS: 00010046
  RAX: 0000000000000000 RBX: ffff95e48e025c00 RCX: 0000000000000000
  RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff95e48e025c00
  RBP: ffff95e4bf3660a4 R08: 0000000000000000 R09: ffffffff86d5e100
  R10: ffff95e49e1de600 R11: 0000000000000001 R12: ffff95e4bf366180
  R13: ffff95e48e025c00 R14: ffff95e4bf366028 R15: ffff95e4bf366000
  FS:  0000000000000000(0000) GS:ffff95e4df200000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: ffffffffffffffd6 CR3: 0000000f86a0a003 CR4: 00000000001606f0
  Call Trace:
   receive_context_interrupt+0x1f/0x40 [hfi1]
   __free_irq+0x201/0x300
   free_irq+0x2e/0x60
   pci_free_irq+0x18/0x30
   msix_free_irq.part.2+0x46/0x80 [hfi1]
   msix_clean_up_interrupts+0x2b/0x70 [hfi1]
   hfi1_init_dd+0x640/0x1a90 [hfi1]
   do_init_one.isra.19+0x34d/0x680 [hfi1]
   local_pci_probe+0x41/0x90
   work_for_cpu_fn+0x16/0x20
   process_one_work+0x1a7/0x360
   worker_thread+0x1cf/0x390
   ? create_worker+0x1a0/0x1a0
   kthread+0x112/0x130
   ? kthread_flush_work_fn+0x10/0x10
   ret_from_fork+0x35/0x40

The free_irq() results in a callback to the registered interrupt handler,
and rcd->do_interrupt is NULL because the receive context data structures
are not fully initialized.

Fix by ensuring that the do_interrupt is always assigned and adding a
guards in the slow path handler to detect and handle a partially
initialized receive context and noop the receive.

Link: https://lore.kernel.org/r/20211129192003.101968.33612.stgit@awfm-01.cornelisnetworks.com


Cc: stable@vger.kernel.org
Fixes: b0ba3c18 ("IB/hfi1: Move normal functions from hfi1_devdata to const array")
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@cornelisnetworks.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>