Fix the number of frames used when interleaving in AudioBuffer::InterleaveTo()

R=henrik.lundin@webrtc.org, peah@webrtc.org
TBR=tina.legrand@webrtc.org

Review URL: https://codereview.webrtc.org/1862553002 .

Cr-Commit-Position: refs/heads/master@{#12249}
diff --git a/webrtc/modules/audio_processing/audio_buffer.cc b/webrtc/modules/audio_processing/audio_buffer.cc
index f300bb8..f9b9f63 100644
--- a/webrtc/modules/audio_processing/audio_buffer.cc
+++ b/webrtc/modules/audio_processing/audio_buffer.cc
@@ -430,10 +430,10 @@
   }
 
   if (frame->num_channels_ == num_channels_) {
-    Interleave(data_ptr->ibuf()->channels(), proc_num_frames_, num_channels_,
+    Interleave(data_ptr->ibuf()->channels(), output_num_frames_, num_channels_,
                frame->data_);
   } else {
-    UpmixMonoToInterleaved(data_ptr->ibuf()->channels()[0], proc_num_frames_,
+    UpmixMonoToInterleaved(data_ptr->ibuf()->channels()[0], output_num_frames_,
                            frame->num_channels_, frame->data_);
   }
 }