utvideodec: Add a missing include

This was missing from 77c23704c76, fixing building.

Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/utvideodec.c

@@ -33,6 +33,7 @@
 #include "bitstream.h"
 #include "bswapdsp.h"
 #include "bytestream.h"
+#include "internal.h"
 #include "thread.h"
 #include "utvideo.h"