Types and type qualifiers have to be to the right of "operator".

Bug: http://b/110779387
Test: Builds with new toolchain.
Change-Id: I557ef6f8117f181a3d7bf60ee31606a8331d0ee9
diff --git a/libnetdutils/include/netdutils/MemBlock.h b/libnetdutils/include/netdutils/MemBlock.h
index 38ca19a..ce8ac02 100644
--- a/libnetdutils/include/netdutils/MemBlock.h
+++ b/libnetdutils/include/netdutils/MemBlock.h
@@ -53,7 +53,7 @@
     Slice get() const noexcept { return Slice(mData.get(), mLen); }
 
     // Implicit cast to Slice.
-    const operator Slice() const noexcept { return get(); }
+    operator const Slice() const noexcept { return get(); }
 
   private:
     std::unique_ptr<uint8_t[]> mData;