qemuBuildHostNetStr: remove dead code

This function is never called for VIR_DOMAIN_NET_TYPE_HOSTDEV,
and the dead code comment agrees.

Introduced by commit 1dcbef8a.

src/qemu/qemu_command.c

@@ -3723,11 +3723,6 @@ qemuBuildHostNetStr(virDomainNetDefPtr net,
         virBufferAsprintf(&buf, "user%c", type_sep);
         break;
 
-    case VIR_DOMAIN_NET_TYPE_HOSTDEV:
-        /* Should have been handled earlier via PCI/USB hotplug code. */
-        virObjectUnref(cfg);
-        return NULL;
-
     case VIR_DOMAIN_NET_TYPE_VHOSTUSER:
         virBufferAsprintf(&buf, "vhost-user%cchardev=char%s,",
                           type_sep,
@@ -3737,6 +3732,8 @@ qemuBuildHostNetStr(virDomainNetDefPtr net,
                               net->driver.virtio.queues);
         break;
 
+    case VIR_DOMAIN_NET_TYPE_HOSTDEV:
+        /* Should have been handled earlier via PCI/USB hotplug code. */
     case VIR_DOMAIN_NET_TYPE_LAST:
         break;
     }