vfio: Use dev_printk() when possible

Use dev_printk() when possible to make messages consistent with other
device-related messages.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>