go/types: fix certain vet warnings

Updates #11041

Change-Id: I4e1c670d2b7fc04927d77c6f933cee39b7d48b6e
Reviewed-on: https://go-review.googlesource.com/23083Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/go/types/resolver.go

@@ -67,7 +67,7 @@ func (check *Checker) arityMatch(s, init *ast.ValueSpec) {
 			// TODO(gri) avoid declared but not used error here
 		} else {
 			// init exprs "inherited"
-			check.errorf(s.Pos(), "extra init expr at %s", init.Pos())
+			check.errorf(s.Pos(), "extra init expr at %s", check.fset.Position(init.Pos()))
 			// TODO(gri) avoid declared but not used error here
 		}
 	case l > r && (init != nil || r != 1):

src/go/types/stmt.go

@@ -123,7 +123,7 @@ func (check *Checker) multipleDefaults(list []ast.Stmt) {
 		}
 		if d != nil {
 			if first != nil {
-				check.errorf(d.Pos(), "multiple defaults (first at %s)", first.Pos())
+				check.errorf(d.Pos(), "multiple defaults (first at %s)", check.fset.Position(first.Pos()))
 			} else {
 				first = d
 			}