avfilter/af_asyncts: use llabs for int64_t

long may not be 64 bit on all platforms; so labs on int64_t is unsafe.
This fixes a warning reported in:
http://fate.ffmpeg.org/log.cgi?time=20150905071512&log=compile&slot=i386-darwin-clang-polly-3.7

Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit d74123d03e)

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/af_asyncts.c

@@ -205,7 +205,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *buf)
     delta    = pts - s->pts - get_delay(s);
     out_size = avresample_available(s->avr);
 
-    if (labs(delta) > s->min_delta ||
+    if (llabs(delta) > s->min_delta ||
         (s->first_frame && delta && s->first_pts != AV_NOPTS_VALUE)) {
         av_log(ctx, AV_LOG_VERBOSE, "Discontinuity - %"PRId64" samples.\n", delta);
         out_size = av_clipl_int32((int64_t)out_size + delta);