mtmd : fix padding of n_tokens (ggml-org#19930)

Author: ggerganov

tools/mtmd/mtmd-helper.cpp

@@ -248,7 +248,7 @@ int32_t mtmd_helper_decode_image_chunk(
 
     int32_t n_tokens = mtmd_input_chunk_get_n_tokens(chunk);
     int32_t i_batch = 0;
-    int32_t n_img_batches = GGML_PAD(n_tokens, n_batch) / n_batch;
+    int32_t n_img_batches = (n_tokens + n_batch - 1) / n_batch;
     decode_embd_batch batch_embd(encoded_embd, n_tokens, n_pos_per_embd, n_mmproj_embd);
 
     if (mtmd_decode_use_mrope(ctx)) {