binder: fix inconsistent-missing-override warning.

Some functions are marked as "override" while the rest are not.

No functionality change.

Test: TreeHugger
Change-Id: I7bcd785588feba0c514dcb473f29ea92784efee0
diff --git a/libs/binder/IMemory.cpp b/libs/binder/IMemory.cpp
index 222b32c..84805ff 100644
--- a/libs/binder/IMemory.cpp
+++ b/libs/binder/IMemory.cpp
@@ -82,10 +82,10 @@
     explicit BpMemoryHeap(const sp<IBinder>& impl);
     virtual ~BpMemoryHeap();
 
-    virtual int getHeapID() const;
-    virtual void* getBase() const;
-    virtual size_t getSize() const;
-    virtual uint32_t getFlags() const;
+    int getHeapID() const override;
+    void* getBase() const override;
+    size_t getSize() const override;
+    uint32_t getFlags() const override;
     off_t getOffset() const override;
 
 private: