mmdevapi/tests: make sure return value is used (LLVM/Clang)

[Austin English]

-- 
-Austin
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diff --git a/dlls/mmdevapi/tests/mmdevenum.c b/dlls/mmdevapi/tests/mmdevenum.c
index 2ccaa81..98c25a1 100644
--- a/dlls/mmdevapi/tests/mmdevenum.c
+++ b/dlls/mmdevapi/tests/mmdevenum.c
@@ -140,6 +140,7 @@ START_TEST(mmdevenum)
 
     /* Proving that it is static.. */
     hr = CoCreateInstance(&CLSID_MMDeviceEnumerator, NULL, CLSCTX_INPROC_SERVER, &IID_IMMDeviceEnumerator, (void**)&mme2);
+    ok(hr == S_OK, "CoCreateInstance failed: 0x%08x\n", hr);
     IUnknown_Release(mme2);
     ok(mme == mme2, "Pointers are not equal!\n");