create: set f.entry after creating files

After Tcreate on a file, the fid is open and should be usable for
read/write without a separate Topen. Set f.entry via root.Open()
after creation so subsequent reads/writes on the same fid work.

cmd/olliesrv/server.go

@@ -457,6 +457,9 @@ func create(root *fs.Tree, cs *connState, fc *plan9.Fcall) *plan9.Fcall {
 	f.path = newPath
 	f.qid = qid
 	f.mode = fc.Mode
+	if ent, err := root.Open(rel); err == nil {
+		f.entry = ent
+	}
 	return &plan9.Fcall{Type: plan9.Rcreate, Tag: fc.Tag, Qid: qid}
 }