[Bugfix] Fixing division by zero in triton_attn if query_heads/kv_heads > 16 (#23424)

Signed-off-by: Burkhard Ringlein <ngl@zurich.ibm.com>

vllm/attention/ops/triton_unified_attention.py

@@ -674,7 +674,8 @@ def unified_attention(
     num_queries_per_kv = num_query_heads // num_kv_heads
     head_size = q.shape[2]
 
-    BLOCK_M = 16
+    BLOCK_M = 16 if num_queries_per_kv <= 16 else triton.next_power_of_2(
+        num_queries_per_kv)
     BLOCK_Q = BLOCK_M // num_queries_per_kv
 
     # Ideally we would launch with kernel with: