avformat/mpegts: Don't use uninitialized value in av_log()

It is undefined behaviour in (at least) C11 (see C11 6.3.2.1 (2)).
Fixes Coverity issue #1500314.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavformat/mpegts.c

@@ -2189,7 +2189,7 @@ int ff_parse_mpeg2_descriptor(AVFormatContext *fc, AVStream *st, int stream_type
             uint32_t buf;
             AVDOVIDecoderConfigurationRecord *dovi;
             size_t dovi_size;
-            int dependency_pid;
+            int dependency_pid = -1; // Unset
 
             if (desc_end - *pp < 4) // (8 + 8 + 7 + 6 + 1 + 1 + 1) / 8
                 return AVERROR_INVALIDDATA;