avcodec/v4l2_buffers: read height/width from the proper context

Frames are generally dequeued into capture buffers, so using
the output properties here was incorrect. It happened to work
fine for decoding, since the output/capture buffers have the same
dimensions.

For the v4l2 scaler, the dimensions can be different between output
and capture. Using the buffer's associated context makes this code
work correctly regardless of where the frame is coming from.
Signed-off-by: Aman Gupta <aman@tmm1.net>

libavcodec/v4l2_buffers.c

@@ -404,7 +404,6 @@ int ff_v4l2_buffer_avframe_to_buf(const AVFrame *frame, V4L2Buffer *out)
 
 int ff_v4l2_buffer_buf_to_avframe(AVFrame *frame, V4L2Buffer *avbuf)
 {
-    V4L2m2mContext *s = buf_to_m2mctx(avbuf);
     int ret;
 
     av_frame_unref(frame);
@@ -423,8 +422,8 @@ int ff_v4l2_buffer_buf_to_avframe(AVFrame *frame, V4L2Buffer *avbuf)
     frame->pts = v4l2_get_pts(avbuf);
 
     /* these two values are updated also during re-init in v4l2_process_driver_event */
-    frame->height = s->output.height;
-    frame->width = s->output.width;
+    frame->height = avbuf->context->height;
+    frame->width = avbuf->context->width;
 
     /* 3. report errors upstream */
     if (avbuf->buf.flags & V4L2_BUF_FLAG_ERROR) {