Fix NUT (de)muxer warnings:

CC    libavformat/nutdec.o
libavformat/nutdec.c: In function ‘read_seek’:
libavformat/nutdec.c:862: warning: passing argument 3 of ‘av_tree_find’ from incompatible pointer type
./libavutil/tree.h:44: note: expected ‘int (*)(void *, const void *)’ but argument is of type ‘int (*)(struct Syncpoint *, struct Syncpoint *)’
libavformat/nutdec.c:871: warning: passing argument 3 of ‘av_tree_find’ from incompatible pointer type
./libavutil/tree.h:44: note: expected ‘int (*)(void *, const void *)’ but argument is of type ‘int (*)(struct Syncpoint *, struct Syncpoint *)’
libavformat/nutdec.c:879: warning: passing argument 3 of ‘av_tree_find’ from incompatible pointer type
./libavutil/tree.h:44: note: expected ‘int (*)(void *, const void *)’ but argument is of type ‘int (*)(struct Syncpoint *, struct Syncpoint *)’
CC    libavformat/nutenc.o
libavformat/nutenc.c: In function ‘write_packet’:
libavformat/nutenc.c:680: warning: passing argument 3 of ‘av_tree_find’ from incompatible pointer type
./libavutil/tree.h:44: note: expected ‘int (*)(void *, const void *)’ but argument is of type ‘int (*)(struct Syncpoint *, struct Syncpoint *)’

Originally committed as revision 22707 to svn://svn.ffmpeg.org/ffmpeg/trunk