Make find_port return Unit and use Foreachers in ResolveKinds

* Modify for backporting

src/main/scala/firrtl/passes/ResolveKinds.scala

@@ -5,10 +5,13 @@ package firrtl.passes
 import firrtl._
 import firrtl.ir._
 import firrtl.Mappers._
+import firrtl.traversals.Foreachers._
+import firrtl.options.PreservesAll
 
 object ResolveKinds extends Pass {
-  private def find_port(kinds: collection.mutable.HashMap[String, Kind])(p: Port): Port = {
-    kinds(p.name) = PortKind ; p
+
+  private def find_port(kinds: collection.mutable.HashMap[String, Kind])(p: Port): Unit = {
+    kinds(p.name) = PortKind
   }
 
   def resolve_expr(kinds: collection.mutable.HashMap[String, Kind])(e: Expression): Expression = e match {
@@ -31,7 +34,7 @@ object ResolveKinds extends Pass {
 
   def resolve_kinds(m: DefModule): DefModule = {
     val kinds = new collection.mutable.HashMap[String, Kind]
-    m.map(find_port(kinds))
+    m.foreach(find_port(kinds))
     m.map(resolve_stmt(kinds))
   }