core: Fix clang build

Recent changes to the build system that made more warnings be flagged as
errors caused building via clang to break.

Fixes #4795

src/core/file_sys/fsmitm_romfsbuild.cpp

@@ -103,7 +103,7 @@ static u32 romfs_calc_path_hash(u32 parent, std::string_view path, u32 start,
     u32 hash = parent ^ 123456789;
     for (u32 i = 0; i < path_len; i++) {
         hash = (hash >> 5) | (hash << 27);
-        hash ^= path[start + i];
+        hash ^= static_cast<u32>(path[start + i]);
     }
 
     return hash;