partition_data_manager: Take VirtualFile by const reference in constructor

Given the VirtualFile instance isn't stored into the class as a data
member, or written to, this can just be turned into a const reference,
as the constructor doesn't need to make a copy of it.

src/core/crypto/partition_data_manager.h

@@ -23,7 +23,7 @@ class PartitionDataManager {
 public:
     static const u8 MAX_KEYBLOB_SOURCE_HASH;
 
-    explicit PartitionDataManager(FileSys::VirtualDir sysdata_dir);
+    explicit PartitionDataManager(const FileSys::VirtualDir& sysdata_dir);
     ~PartitionDataManager();
 
     // BOOT0