IOS/FS: Make sure FS root directory exists

Previously, the FS root directory would get created as a side
effect of calling CreateDirectory during boot (since the
implementation was sloppy and used File::CreateFullDir).

Since CreateDirectory no longer does that, it is necessary to ensure
that the FS root directory does exist by creating it explicitly.

Source/Core/Core/IOS/FS/HostBackend/FS.cpp

@@ -103,6 +103,7 @@ bool HostFileSystem::FstEntry::CheckPermission(Uid caller_uid, Gid caller_gid,
 
 HostFileSystem::HostFileSystem(const std::string& root_path) : m_root_path{root_path}
 {
+  File::CreateFullPath(m_root_path + "/");
   ResetFst();
   LoadFst();
 }