vfio/pci: add missing identifier name in argument of function prototype

The function prototype is missing an identifier name. Add one.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20210902212631.54260-1-colin.king@canonical.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>