vfio/pci: Remove redundant declaration of vfio_pci_driver

It was added by commit 137e5531 ("vfio/pci: Add sriov_configure
support") but duplicates a forward declaration earlier in the file.

Remove it.

Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>