Fix warnings in NUT demuxer:

Fix warnings in NUT demuxer:

libavformat/nutdec.c: In function ‘read_seek’:
libavformat/nutdec.c:862: warning: passing argument 4 of ‘av_tree_find’ from incompatible pointer type
./libavutil/tree.h:44: note: expected ‘void **’ but argument is of type ‘struct Syncpoint **’
libavformat/nutdec.c:871: warning: passing argument 4 of ‘av_tree_find’ from incompatible pointer type
./libavutil/tree.h:44: note: expected ‘void **’ but argument is of type ‘struct Syncpoint **’

Originally committed as revision 22662 to svn://svn.ffmpeg.org/ffmpeg/trunk