dca: set AVCodecContext frame_size for DTS audio

Set the frame size when decoding DTS audio.

This has the side effect of fixing the computation of timestamps for DTS-HD in compute_pkt_fields.  Since frame_size is
not currently set, the duration of a frame is being guessed based on the streams bitrate.  But for DTS-HD, the bitrate
currently used is the rate of the DTS core which is much different than the whole DTS-HD stream and leads to a wildly
inaccurate frame duration estimate.

Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>
(cherry picked from commit 49c7006c7e)

Signed-off-by: Anton Khirnov <anton@khirnov.net>
(cherry picked from commit 0631896885)

Signed-off-by: Reinhard Tartler <siretart@tauware.de>

libavcodec/dca.c

@@ -1224,6 +1224,7 @@ static int dca_decode_frame(AVCodecContext * avctx,
     //set AVCodec values with parsed data
     avctx->sample_rate = s->sample_rate;
     avctx->bit_rate = s->bit_rate;
+    avctx->frame_size = s->sample_blocks * 32;
 
     channels = s->prim_channels + !!s->lfe;