fix flashmaskv2 maxmin buffer padding (#74881)

Author: umiswing

paddle/phi/kernels/gpu/flash_attn_v3_grad_kernel.cu

@@ -1190,7 +1190,7 @@ void FlashMaskV2GradBaseKernel(
     // TODO(umiswing): refine this block constraint (kBlockN % 32), since some
     // of kBlockN is not divisible by 32 flashmask_maxmin_shape[2] =
     // (flashmask_maxmin_shape[2] + 31) / 32 * 8;
-    flashmask_maxmin_shape[2] = (flashmask_maxmin_shape[2] + 31) / 32;
+    flashmask_maxmin_shape[2] = ((flashmask_maxmin_shape[2] + 31) / 32 + 3) / 4 * 4;
     flashmask_maxmin_shape[3] = 8;
 
     flashmask_maxmin.set_type(phi::DataType::INT32);

paddle/phi/kernels/gpu/flash_attn_v3_kernel.cu

@@ -1965,7 +1965,7 @@ void FlashMaskV2BaseKernel(
     // TODO(umiswing): refine this block constraint (kBlockN % 32), since some
     // of kBlockN is not divisible by 32 flashmask_maxmin_shape[2] =
     // (flashmask_maxmin_shape[2] + 31) / 32 * 8;
-    flashmask_maxmin_shape[2] = ((flashmask_maxmin_shape[2] + 31) / 32 + 3) / 4;
+    flashmask_maxmin_shape[2] = ((flashmask_maxmin_shape[2] + 31) / 32 + 3) / 4 * 4;
     flashmask_maxmin_shape[3] = 8;
 
     flashmask_maxmin.set_type(phi::DataType::INT32);