StorageManager: Add missing const in member functions

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

libraries/StorageManager/StorageManager.cpp

@@ -292,7 +292,7 @@ void StorageAccess::write_uint32(uint16_t loc, uint32_t value) const
 /*
   copy one area to another
  */
-bool StorageAccess::copy_area(const StorageAccess &source)
+bool StorageAccess::copy_area(const StorageAccess &source) const
 {
     // we deliberately allow for copies from smaller areas. This
     // allows for a partial backup region for parameters

libraries/StorageManager/StorageManager.h

@@ -102,7 +102,7 @@ public:
     void write_uint32(uint16_t loc, uint32_t value) const;
 
     // copy from one storage area to another
-    bool copy_area(const StorageAccess &source);
+    bool copy_area(const StorageAccess &source) const;
 
 private:
     const StorageManager::StorageType type;