core: Simplify SDMC mod loading

If someone else wants to support other mod formats in the SDMC
directory, that can be added later. For now, just allow RomFS modding
here and force people to do other types of mods the old way.

Addresses review comments.

Co-authored-by: LC <mathew1800@gmail.com>

src/core/hle/service/filesystem/filesystem.cpp

@@ -706,8 +706,9 @@ FileSys::VirtualDir FileSystemController::GetModificationLoadRoot(u64 title_id)
 FileSys::VirtualDir FileSystemController::GetSDMCModificationLoadRoot(u64 title_id) const {
     LOG_TRACE(Service_FS, "Opening SDMC mod load root for tid={:016X}", title_id);
 
-    if (sdmc_factory == nullptr)
+    if (sdmc_factory == nullptr) {
         return nullptr;
+    }
 
     return sdmc_factory->GetSDMCModificationLoadRoot(title_id);
 }