bmc: remove redundant ‘std::move’ call

```
../bmc/file_handler.cpp:70:21: error: redundant move in return statement [-Werror=redundant-move]
   70 |     return std::move(ret);
      |            ~~~~~~~~~^~~~~
../bmc/file_handler.cpp:70:21: note: remove ‘std::move’ call
cc1plus: all warnings being treated as errors
```

Change-Id: I07b7ac5c715a53fc5d78cba5dba4aa5b7407304c
Signed-off-by: Willy Tu <wltu@google.com>
diff --git a/bmc/file_handler.cpp b/bmc/file_handler.cpp
index d2452ba..829f92c 100644
--- a/bmc/file_handler.cpp
+++ b/bmc/file_handler.cpp
@@ -67,7 +67,7 @@
     {
         return std::nullopt;
     }
-    return std::move(ret);
+    return ret;
 }
 
 int FileHandler::getSize()