avcodec/error_resilience: Constify ThreadFrame*

Forgotten in 0eb399ac3953da16f880a1e455bb009a45f76d49.
While just at it, also use a forward declaration.

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/error_resilience.h

@@ -24,7 +24,6 @@
 
 #include "avcodec.h"
 #include "me_cmp.h"
-#include "threadframe.h"
 
 ///< current MB is the first after a resync marker
 #define VP_START               1
@@ -40,7 +39,7 @@
 
 typedef struct ERPicture {
     AVFrame *f;
-    ThreadFrame *tf;
+    const struct ThreadFrame *tf;
 
     // it is the caller's responsibility to allocate these buffers
     int16_t (*motion_val[2])[2];

libavcodec/h264dec.h

@@ -43,6 +43,7 @@
 #include "h264qpel.h"
 #include "h274.h"
 #include "mpegutils.h"
+#include "threadframe.h"
 #include "videodsp.h"
 
 #define H264_MAX_PICTURE_COUNT 36