gofmt: simpler walkDir

Swapping the goroutines lets them reuse the
communication completion on v instead of
needing a second channel (done).

R=gri
CC=golang-dev
https://golang.org/cl/4287045

src/cmd/gofmt/gofmt.go

@@ -158,21 +158,16 @@ func (v fileVisitor) VisitFile(path string, f *os.FileInfo) {
 
 
 func walkDir(path string) {
-	// start an error handler
-	done := make(chan bool)
 	v := make(fileVisitor)
 	go func() {
+		filepath.Walk(path, v, v)
+		close(v)
+	}()
 	for err := range v {
 		if err != nil {
 			report(err)
 		}
 	}
-		done <- true
-	}()
-	// walk the tree
-	filepath.Walk(path, v, v)
-	close(v) // terminate error handler loop
-	<-done   // wait for all errors to be reported
 }