Assign default SCSI controller model before checking attribute validity

If the qemu binary on x86 does not support lsi SCSI controller,
but it supports virtio-scsi, we reject the virtio-specific attributes
for no reason.

Move the default controller assignment before the check.

https://bugzilla.redhat.com/show_bug.cgi?id=1168849

src/qemu/qemu_command.c

@@ -4353,10 +4353,15 @@ qemuBuildControllerDevStr(virDomainDefPtr domainDef,
                           int *nusbcontroller)
 {
     virBuffer buf = VIR_BUFFER_INITIALIZER;
-    int model;
+    int model = def->model;
+
+    if (def->type == VIR_DOMAIN_CONTROLLER_TYPE_SCSI) {
+        if ((qemuSetSCSIControllerModel(domainDef, qemuCaps, &model)) < 0)
+            return NULL;
+    }
 
     if (!(def->type == VIR_DOMAIN_CONTROLLER_TYPE_SCSI &&
-          def->model == VIR_DOMAIN_CONTROLLER_MODEL_SCSI_VIRTIO_SCSI)) {
+          model == VIR_DOMAIN_CONTROLLER_MODEL_SCSI_VIRTIO_SCSI)) {
         if (def->queues) {
             virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
                            _("'queues' is only supported by virtio-scsi controller"));
@@ -4376,10 +4381,6 @@ qemuBuildControllerDevStr(virDomainDefPtr domainDef,
 
     switch (def->type) {
     case VIR_DOMAIN_CONTROLLER_TYPE_SCSI:
-        model = def->model;
-        if ((qemuSetSCSIControllerModel(domainDef, qemuCaps, &model)) < 0)
-            return NULL;
-
         switch (model) {
         case VIR_DOMAIN_CONTROLLER_MODEL_SCSI_VIRTIO_SCSI:
             if (def->info.type == VIR_DOMAIN_DEVICE_ADDRESS_TYPE_CCW)