go/types: fix doc string for Named.Obj

Fixes #19249.

Change-Id: I6327192eca11fa24f1078c016c9669e4ba4bdb4e
Reviewed-on: https://go-review.googlesource.com/37399Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/go/types/type.go

@@ -394,7 +394,7 @@ func NewNamed(obj *TypeName, underlying Type, methods []*Func) *Named {
 	return typ
 }
 
-// TypeName returns the type name for the named type t.
+// Obj returns the type name for the named type t.
 func (t *Named) Obj() *TypeName { return t.obj }
 
 // NumMethods returns the number of explicit methods whose receiver is named type t.