KVM: x86: Nullify irqfd->producer if updating IRTE for bypass fails

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Nullify irqfd->producer if updating IRTE for bypass fails Nullify irqfd->producer if updating the IRTE for bypass fails, as leaving a dangling pointer will result in a use-after-free if the irqfd is reachable through KVM's routing, but the producer is freed separately. E.g. for VFIO PCI, the producer is embedded in struct "vfio_pci_irq_ctx" and freed when the vector is disabled, which can happen independent of routing updates. [sean: drop PPC change, massage changelog]