encoding/asn1: fix unused assignments

Unused assignment for `err` encoding/asn1/marshal.go:622:3
Unused assignment for `err` encoding/asn1/marshal.go:650:5

Change-Id: I4226238645ce3640f25124cb405444e61439fd3f
Reviewed-on: https://go-review.googlesource.com/13847Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/encoding/asn1/marshal.go

@@ -627,7 +627,7 @@ func marshalField(out *forkableWriter, v reflect.Value, params fieldParameters)
 		})
 	}
 
-	return nil
+	return err
 }
 
 // Marshal returns the ASN.1 encoding of val.
@@ -648,5 +648,5 @@ func Marshal(val interface{}) ([]byte, error) {
 		return nil, err
 	}
 	_, err = f.writeTo(&out)
-	return out.Bytes(), nil
+	return out.Bytes(), err
 }