Fix multihead op bug. (#20783)

The op should handle k=1024

test=develop
Signed-off-by: Nzhaoyuchen <zhaoyuchen01@baidu.com>

paddle/fluid/operators/multihead_matmul_op.cc

@@ -134,7 +134,7 @@ MultiHeadMatMul Operator.
 This op is used for optimize multi head calculation in ernie model.
 Not suggest to use in other case except has same structure as ernie.
 
-Example of matrix multiplication with head_number of H
+Example of matrix multiplication with head_number of B
 - X: [B, M, K], Y: [B, K, N] => Out: [B, M, N]
 
 Both the input `Q` and `K` can carry the LoD (Level of Details) information,

paddle/fluid/operators/multihead_matmul_op.cu

@@ -331,7 +331,7 @@ void MultiHeadGPUCompute(const platform::CUDADeviceContext &dev_ctx,
   auto stream = dev_ctx.stream();
 
   int grid = m;
-  PADDLE_ENFORCE_LT(k, 1024,
+  PADDLE_ENFORCE_LE(k, 1024,
                     "Input head_number * size_per_head should <= 1024");
   int block = k <= 1024 ? k : 1024;
   add_QKV<T><<<grid, block, 0, stream>>>(Q, K, V, q_buf, k_buf, v_buf, bias_q,