bhyve: Enable virtio-scsi legacy config parsing.

The previous commit added the handler to parse the command line
options for virtio-scsi devices but forgot to set the correct function
pointer to point to the handler.

Reported by:	vangyzen
Reviewed by:	vangyzen
Fixes:		621b509048
Differential Revision:	https://reviews.freebsd.org/D29438

usr.sbin/bhyve/pci_virtio_scsi.c

@@ -739,6 +739,7 @@ pci_vtscsi_init(struct vmctx *ctx, struct pci_devinst *pi, nvlist_t *nvl)
 struct pci_devemu pci_de_vscsi = {
 	.pe_emu =	"virtio-scsi",
 	.pe_init =	pci_vtscsi_init,
+	.pe_legacy_config = pci_vtscsi_legacy_config,
 	.pe_barwrite =	vi_pci_write,
 	.pe_barread =	vi_pci_read
 };