layers: Suppress warning generation after app acknowledges an error

The app already knows about the problem-- it has requested that the call
be skipped. Producing another warning afterward is just noise.

Signed-off-by: Chris Forbes <chrisforbes@google.com>
diff --git a/layers/parameter_validation_utils.h b/layers/parameter_validation_utils.h
index 4fe740c..099018e 100644
--- a/layers/parameter_validation_utils.h
+++ b/layers/parameter_validation_utils.h
@@ -796,7 +796,7 @@
 * @param value VkResult value to validate.
 */
 static void validate_result(debug_report_data *report_data, const char *apiName, VkResult result) {
-    if (result < 0) {
+    if (result < 0 && result != VK_ERROR_VALIDATION_FAILED_EXT) {
         std::string resultName = string_VkResult(result);
 
         if (resultName == UnsupportedResultString) {