[examples] Fix stale thread layout comment in wgmma_sm90.cu

[SriRangaTarun]

Summary

Fixes #3340.

In the NT GEMM setup in examples/cute/tutorial/hopper/wgmma_sm90.cu, the
copyA and copyB tiled copies are both constructed from
Layout<Shape<_16,_8>>, but the trailing comments describe them as
Thr layout 32x4. The comments appear to be left over from an earlier
thread arrangement.

The TN setup further down the same file constructs the same
Layout<Shape<_16,_8>, Stride<_8,_1>> and annotates it Thr layout 16x8,
which confirms the intended convention.

Change

Comment-only; updates both annotations from 32x4 to 16x8. No functional
change and nothing to rebuild.

Since this is a tutorial example, the annotations are load-bearing for
readers learning to map make_tiled_copy arguments onto thread/value
layouts — a mismatch here is more costly than in ordinary source.