tests: Use mobile-friendly DS format

Update InvalidUsageBits test to use D24_UNORM_S8_UINT which
can run on mobile and desktop HW. Long-term need a format helper
to choose from class of format based on device, but for now just
trying to use a format that will work for at least one mobile
and desktop target.
diff --git a/tests/layer_validation_tests.cpp b/tests/layer_validation_tests.cpp
index 34241be..31faafa 100644
--- a/tests/layer_validation_tests.cpp
+++ b/tests/layer_validation_tests.cpp
@@ -2240,7 +2240,7 @@
     ASSERT_NO_FATAL_FAILURE(InitState());
     VkImageObj image(m_device);
     // Initialize image with USAGE_INPUT_ATTACHMENT
-    image.init(128, 128, VK_FORMAT_D32_SFLOAT_S8_UINT,
+    image.init(128, 128, VK_FORMAT_D24_UNORM_S8_UINT,
                VK_IMAGE_USAGE_INPUT_ATTACHMENT_BIT, VK_IMAGE_TILING_OPTIMAL, 0);
     ASSERT_TRUE(image.initialized());