vfio/pci: Cleanup vfio_early_setup_msix() error path

With the addition of the Chelsio quirk we have an error path out of
vfio_early_setup_msix() that doesn't free the allocated VFIOMSIXInfo
struct.  This doesn't introduce a leak as it still gets freed in the
vfio_put_device() path, but it's complicated and sloppy to rely on
that.  Restructure to free the allocated data on error and only link
it into the vdev on success.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reported-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
