The MMA expects Q sub-tiles from a full (128,HD) canonical buffer,
but we were only loading (128,16) sub-tiles into a (128,16) buffer.
The MMA descriptor with block_mn=128 describes a (128,128) matrix,
reading 128 columns from SMEM but only 16 had real data.
Now: load all HD/16 TMA tiles of Q into a full (128,HD) canonical
buffer before the QK loop. The MMA reads the kt-th sub-tile via
descriptor offset kt * 128 * 32 bytes.
Also: share single sTmaBuf staging buffer for all TMA loads (Q, K, V).
Removed separate sQ_tma, sK_tma, sV_tma buffers.
biondizzle
204cc90808