[lsan][Fuchsia] Fix bounds checking for thread_local allocator cache when scanning TLS regions

When scanning over TLS regions, we attempt to check if one of the regions is
one of the thread_local allocator caches which would be located in one of the
TLS blocks pointer to by the DTV. This is to prevent marking a pointer that was
allocated by the primary allocator (from a thread_local cache) as reachable. The
check is a simple bounds check to see if the allocator cache is within the
bounds of one of the TLS block we're iterating over, but it looks like the check
for the end of the cache is slightly incorrect.

Differential Revision: https://reviews.llvm.org/D156015