lavc/dvdec: drop the only use of DVVideoContext.avctx

The function gets the codec context parameter directly.

libavcodec/dvdec.c

@@ -391,7 +391,7 @@ static int dv_decode_video_segment(AVCodecContext *avctx, void *arg)
     LOCAL_ALIGNED_16(int16_t, sblock, [5 * DV_MAX_BPM], [64]);
     LOCAL_ALIGNED_16(uint8_t, mb_bit_buffer, [80     + AV_INPUT_BUFFER_PADDING_SIZE]); /* allow some slack */
     LOCAL_ALIGNED_16(uint8_t, vs_bit_buffer, [80 * 5 + AV_INPUT_BUFFER_PADDING_SIZE]); /* allow some slack */
-    const int log2_blocksize = 3-s->avctx->lowres;
+    const int log2_blocksize = 3 - avctx->lowres;
     int is_field_mode[5];
     int vs_bit_buffer_damaged = 0;
     int mb_bit_buffer_damaged[5] = {0};