Simplify: use FFMIN

Originally committed as revision 20213 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/aviobuf.c

@@ -107,9 +107,7 @@ void put_buffer(ByteIOContext *s, const unsigned char *buf, int size)
     int len;
 
     while (size > 0) {
-        len = (s->buf_end - s->buf_ptr);
-        if (len > size)
-            len = size;
+        len = FFMIN(s->buf_end - s->buf_ptr, size);
         memcpy(s->buf_ptr, buf, len);
         s->buf_ptr += len;