[BUG] vDPA/ifcvf: got a warning when removing the module

[Zheyu Ma]

Hello,

I found a bug in the ifcvf driver.
When removing the module, I got the following warning:

[   14.478123] general protection fault, probably for non-canonical
address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN PTI
[   14.478701] KASAN: null-ptr-deref in range
[0x0000000000000028-0x000000000000002f]
[   14.479922] RIP: 0010:vdpa_mgmtdev_unregister+0x39/0x150
[   14.484063] Call Trace:
[   14.484186]  <TASK>
[   14.484292]  ? _raw_spin_unlock_irqrestore+0x3d/0x60
[   14.484536]  ifcvf_remove+0x3a/0x50 [ifcvf]
[   14.484743]  pci_device_remove+0x92/0x240

The reason is that the 'ifcvf_mgmt_dev' is zero which means that
ifcvf_vdpa_dev_add() was not executed.
Since I am not familiar with the driver, I cannot find a proper solution for it.

Zheyu Ma