savedata_archive: Make GetFreeBytes return a more accurate value

Previously, we were returning a value that was way too big, causing an integer overflow in Fractured Souls.
According to wwylele, the biggest oberserved save size for 3DS is 1MB, so this new value should leave plenty of room, even if games use a bigger size.

src/core/file_sys/savedata_archive.cpp

@@ -351,8 +351,8 @@ ResultVal<std::unique_ptr<DirectoryBackend>> SaveDataArchive::OpenDirectory(
 }
 
 u64 SaveDataArchive::GetFreeBytes() const {
-    // TODO: Stubbed to return 1GiB
+    // TODO: Stubbed to return 32MiB
-    return 1024 * 1024 * 1024;
+    return 1024 * 1024 * 32;
 }
 
 } // namespace FileSys