IFF: move ff_cmap_read_palette() prototype to a header file

Originally committed as revision 22307 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/iff.c

@@ -27,6 +27,7 @@
 #include "bytestream.h"
 #include "avcodec.h"
 #include "get_bits.h"
+#include "iff.h"
 
 typedef struct {
     AVFrame frame;