virtio-pci: fix the confusing error message

The error message on the failure of pfn check should tell
virtio-pci rather than virtio-mmio, just fix it.

Signed-off-by: Michael Wang <yun.wang@linux.alibaba.com>
Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://lore.kernel.org/r/ae5e154e-ac59-f0fa-a7c7-091a2201f581@linux.alibaba.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>