whisper : fix extra memory usage (#2534)

* passing samples_padded by ref to the threads.

* passing samples_padded by ref to the threads.

---------

Co-authored-by: Vinith Misra <[email protected]>

src/whisper.cpp

@@ -3164,7 +3164,7 @@ static bool log_mel_spectrogram(
         std::vector<std::thread> workers(n_threads - 1);
         for (int iw = 0; iw < n_threads - 1; ++iw) {
             workers[iw] = std::thread(
-                    log_mel_spectrogram_worker_thread, iw + 1, hann, samples_padded,
+                    log_mel_spectrogram_worker_thread, iw + 1, hann, std::cref(samples_padded),
                     n_samples + stage_2_pad, frame_size, frame_step, n_threads,
                     std::cref(filters), std::ref(mel));
         }