decklink: fix macos werror build

decklink: fix macos werror build

../sys/decklink/gstdecklink.cpp:1703:7: error: format specifies type 'long' but the argument has type 'int64_t' (aka 'long long') [-Werror,-Wformat]
      persistent_id);
      ^~~~~~~~~~~~~~
/Library/Frameworks/GStreamer.framework/Versions/1.0/include/gstreamer-1.0/gst/gstinfo.h:1070:87: note: expanded from macro 'GST_DEBUG'
#define GST_DEBUG(...)                  GST_CAT_LEVEL_LOG (GST_CAT_DEFAULT, GST_LEVEL_DEBUG,   NULL, __VA_ARGS__)
                                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
/Library/Frameworks/GStreamer.framework/Versions/1.0/include/gstreamer-1.0/gst/gstinfo.h:646:31: note: expanded from macro 'GST_CAT_LEVEL_LOG'
        (GObject *) (object), __VA_ARGS__);                             \
                              ^~~~~~~~~~~