Correct S4U2Self spelling in a comment

Signed-off-by: Isaac Boukris <iboukris@gmail.com>

kdc/krb5tgs.c

@@ -2056,7 +2056,7 @@ server_lookup:
 			ret = KRB5KDC_ERR_C_PRINCIPAL_UNKNOWN;
 		    msg = krb5_get_error_message(context, ret);
 		    kdc_log(context, config, 1,
-			    "S2U4Self principal to impersonate %s not found in database: %s",
+			    "S4U2Self principal to impersonate %s not found in database: %s",
 			    tpn, msg);
 		    krb5_free_error_message(context, msg);
 		    goto out;