vfio/pci: Fix incorrect error message

When the "No host device provided" error occurs, the hint message
that starts with "Use -vfio-pci," makes no sense, since "-vfio-pci"
is not a valid command line parameter.

Correct this by replacing "-vfio-pci" with "-device vfio-pci".

Signed-off-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
