avcodec/rv20enc: use MpegEncContext->picture_number instead of encode function parameter

They should be the same and that is what most encode functions use.

Signed-off-by: Marton Balint <cus@passwd.hu>

libavcodec/rv20enc.c

@@ -39,7 +39,7 @@ void ff_rv20_encode_picture_header(MpegEncContext *s, int picture_number){
     put_bits(&s->pb, 1, 0);     /* unknown bit */
     put_bits(&s->pb, 5, s->qscale);
 
-    put_sbits(&s->pb, 8, picture_number); //FIXME wrong, but correct is not known
+    put_sbits(&s->pb, 8, s->picture_number); //FIXME wrong, but correct is not known
     s->mb_x= s->mb_y= 0;
     ff_h263_encode_mba(s);