axi4: don't map unused masters into TL source ID space

src/main/scala/uncore/axi4/ToTL.scala

@@ -13,7 +13,7 @@ case class AXI4ToTLNode() extends MixedAdapterNode(AXI4Imp, TLImp)(
     masters.foreach { m => require (m.maxFlight.isDefined, "AXI4 must include a transaction maximum per ID to convert to TL") }
     val maxFlight = masters.map(_.maxFlight.get).max
     TLClientPortParameters(
-      clients = masters.flatMap { m =>
+      clients = masters.filter(_.maxFlight != Some(0)).flatMap { m =>
         for (id <- m.id.start until m.id.end)
           yield TLClientParameters(
             name        = s"${m.name} ID#${id}",