crypto/openpgp/packet: fix testing print (missing arg)

R=agl
CC=golang-dev
https://golang.org/cl/4173062
diff --git a/src/pkg/crypto/openpgp/packet/symmetrically_encrypted_test.go b/src/pkg/crypto/openpgp/packet/symmetrically_encrypted_test.go
index ee5a30d..5543b20 100644
--- a/src/pkg/crypto/openpgp/packet/symmetrically_encrypted_test.go
+++ b/src/pkg/crypto/openpgp/packet/symmetrically_encrypted_test.go
@@ -54,7 +54,7 @@
 
 		err = mdcReader.Close()
 		if err != nil {
-			t.Errorf("stride: %d, error on Close: %s", err)
+			t.Errorf("stride: %d, error on Close: %s", stride, err)
 		}
 	}