logd: add missing static to CompressionEngine

Test: build
Change-Id: I8b068e137835ce5e1ce2af1911f557cbcaca0fa2
diff --git a/logd/CompressionEngine.cpp b/logd/CompressionEngine.cpp
index f37208b..f9c5979 100644
--- a/logd/CompressionEngine.cpp
+++ b/logd/CompressionEngine.cpp
@@ -23,7 +23,7 @@
 #include <zstd.h>
 
 CompressionEngine& CompressionEngine::GetInstance() {
-    CompressionEngine* engine = new ZstdCompressionEngine();
+    static CompressionEngine* engine = new ZstdCompressionEngine();
     return *engine;
 }