Use TCU_CHECK instead of DE_ASSERT

DE_ASSERT is optimized away in release build. In this case it resulted
in the 'modifyXor' function not being called, causing the reference
memory to go out of sync with the actual memory.

(cherry picked from commit 8b9bed7d58e73412eeb361b612a51b89d1f30978)

Bug: 29044372
Change-Id: I1cf5a5d756cc000dfa0d5fa55535865e13717442
diff --git a/external/vulkancts/modules/vulkan/memory/vktMemoryMappingTests.cpp b/external/vulkancts/modules/vulkan/memory/vktMemoryMappingTests.cpp
index 9bd06ec..ea650d5 100644
--- a/external/vulkancts/modules/vulkan/memory/vktMemoryMappingTests.cpp
+++ b/external/vulkancts/modules/vulkan/memory/vktMemoryMappingTests.cpp
@@ -556,7 +556,7 @@
 		const deUint8	mask	= rng.getUint8();
 
 		((deUint8*)m_ptr)[pos]	= val ^ mask;
-		DE_ASSERT(m_reference.modifyXor((size_t)(m_range.offset + pos), val, mask));
+		TCU_CHECK(m_reference.modifyXor((size_t)(m_range.offset + pos), val, mask));
 	}
 }