tests: Fix RenderPassClearOpMismatch

Change-Id: Ic87bcf65452a8181dfb97f1a284a495752689ad9
diff --git a/tests/layer_validation_tests.cpp b/tests/layer_validation_tests.cpp
index eab5524..ab1c4f3 100644
--- a/tests/layer_validation_tests.cpp
+++ b/tests/layer_validation_tests.cpp
@@ -8190,7 +8190,7 @@
     rpci.pSubpasses = &subpass;
     rpci.attachmentCount = 1;
     VkAttachmentDescription attach_desc = {};
-    attach_desc.format = VK_FORMAT_UNDEFINED;
+    attach_desc.format = VK_FORMAT_B8G8R8A8_UNORM;
     // Set loadOp to CLEAR
     attach_desc.loadOp = VK_ATTACHMENT_LOAD_OP_CLEAR;
     rpci.pAttachments = &attach_desc;