Fix `error: unused variable 'device_buffer'` from `cts_test_base.h` (#18831)

runtime/src/iree/hal/cts/cts_test_base.h

diff --git a/runtime/src/iree/hal/cts/cts_test_base.h b/runtime/src/iree/hal/cts/cts_test_base.h
index 1cb1e52..8799817 100644
--- a/runtime/src/iree/hal/cts/cts_test_base.h
+++ b/runtime/src/iree/hal/cts/cts_test_base.h
@@ -172,7 +172,9 @@
         IREE_HAL_BUFFER_USAGE_DISPATCH_STORAGE | IREE_HAL_BUFFER_USAGE_TRANSFER;
     iree_hal_buffer_t* device_buffer = NULL;
     IREE_ASSERT_OK(iree_hal_allocator_allocate_buffer(
-        iree_hal_device_allocator(device_), params, buffer_size, out_buffer));
+        iree_hal_device_allocator(device_), params, buffer_size,
+        &device_buffer));
+    *out_buffer = device_buffer;
   }
 
   void CreateZeroedDeviceBuffer(iree_device_size_t buffer_size,