Add missing mutex lock

Bug: N/A
Test: mma
Change-Id: I605ce74459de025640dd8be2e68e66384e9c685b
diff --git a/nn/common/ExecutionBurstServer.cpp b/nn/common/ExecutionBurstServer.cpp
index 599f57d..b29f57b 100644
--- a/nn/common/ExecutionBurstServer.cpp
+++ b/nn/common/ExecutionBurstServer.cpp
@@ -495,6 +495,7 @@
 }
 
 Return<void> ExecutionBurstServer::freeMemory(int32_t slot) {
+    std::lock_guard<std::mutex> hold(mMutex);
     mExecutorWithCache->removeCacheEntry(slot);
     return Void();
 }