libvpxdec: Fix "error: implicit declaration of function ‘av_check_image_size’".

av_check_image_size() is declared in libavcore/imgutils.h.

Originally committed as revision 24717 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/libvpxdec.c

@@ -27,6 +27,7 @@
 #include <vpx/vpx_decoder.h>
 #include <vpx/vp8dx.h>
 
+#include "libavcore/imgutils.h"
 #include "avcodec.h"
 
 typedef struct VP8DecoderContext {