virtio_pci: fix cpu affinity support

virtio_pci: fix cpu affinity support

Commit 42e17b04 ("Revert "virtio_pci: use shared interrupts for
virtqueues"") removed the adjustment of the pre_vectors for the virtio
MSI-X vector allocation which was added in commit 3af3221c ("virtio:
allow drivers to request IRQ affinity when creating VQs"). This will
lead to an incorrect assignment of MSI-X vectors, and potential
deadlocks when offlining cpus.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Fixes: 42e17b04 ("Revert "virtio_pci: use shared interrupts for virtqueues")
Reported-by: YASUAKI ISHIMATSU <yasu.isimatu@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>