x/crypto/ssh/agent: ecdsa key/cert typo

Introduced by me in 21536

Change-Id: I4a5f3507270a3d6eea9779508642ea5789d1efca
Reviewed-on: https://go-review.googlesource.com/24811
Reviewed-by: Han-Wen Nienhuys <hanwen@google.com>
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

ssh/agent/server_test.go

@@ -150,6 +150,9 @@ func TestKeyTypes(t *testing.T) {
 		if err := addKeyToAgent(v); err != nil {
 			t.Errorf("error adding key type %s, %v", k, err)
 		}
+		if err := addCertToAgentSock(v, nil); err != nil {
+			t.Errorf("error adding key type %s, %v", k, err)
+		}
 	}
 }