r3d: Fix pos type

avio_tell can return a negative number.

Bug-Id: CID 1265715
CC: libav-stable@libav.org

libavformat/r3d.c

@@ -219,7 +219,7 @@ static int r3d_read_redv(AVFormatContext *s, AVPacket *pkt, Atom *atom)
     AVStream *st = s->streams[0];
     int tmp;
     int av_unused tmp2;
-    uint64_t pos = avio_tell(s->pb);
+    int64_t pos = avio_tell(s->pb);
     unsigned dts;
     int ret;
 
@@ -274,7 +274,7 @@ static int r3d_read_reda(AVFormatContext *s, AVPacket *pkt, Atom *atom)
     AVStream *st = s->streams[1];
     int av_unused tmp, tmp2;
     int samples, size;
-    uint64_t pos = avio_tell(s->pb);
+    int64_t pos = avio_tell(s->pb);
     unsigned dts;
     int ret;